Just thought I would make a thread for people to post the secrets they found. That way, other people can use it for reference, to see which ones they missed or for those perfectionists that don't want to miss them the first time round. I will edit this post as I play through the game to include them as I find them. Before you post, make sure the secret you're adding hasn't already been added in another post so the thread stays an efficient resource and doesn't become overcrowded with repeat posts of the same information. As far, these are the ones I've found.
Episode 1, Level 1: Cradle to Grave (11 Secrets+1 Super Secret)
1. The first gray stone on you're right when you exit your grave can be opened for flare pistol ammo
2. The large, rounded corner stone in this same area can be opened for a box of TNT
3. In the area with the very first zombie is a hedge. The right side of this hedge opens up to a small area containing a body armor.
4. The stone at the front of the chapel in the mortuary. It seems to be triggered to open by stepping on a certain spot in floor. The stone will lower to reveal flare pistol ammo and several rats.
5. Play the piano/organ just behind the curtain. The wall above it will open and contains a Beast Vision item.
6. The Furnace in the Crematorium contains a Life Seed
7. One of the green crypt covers can be blown open with TNT and contains a body armor.
8. Break the window in the upper hallway and jump out onto the fence. Walk along it (but make sure to jump the gap) to reach the roof of the small outside crypt which has a double weapon powerup
9. The next hallway after that window. Hit the light switch to light up the hall and look slightly to the upper-left. One of the crypts has no front. Jump into it for Fire Armor and rats.
Episode 1, Mission 2: Wrong Side of the Tracks (8 Secrets)
1. In the Train station, in the same payphone bank as the ringing phone, one of the phones slides down to reveal a basic armor
2. In the kitchen of the train station bar, blow up the fire extinguisher on the wall to rip open the wall and reveal a small area with a box of flares, a case of TNT and a zombie.
3. In the freezer of the train station kitchen, activate the bloody handprint on the wall to slide back one of the wine shelves in the previously mentioned secret and reveal a limited invisibility powerup
4 and 5. In the train station Book and Map store, activate the cash register to slide down two shelves, one directly in front of you, containing a Doctor's Bag and the other in the back right corner, containing a body armor
6. In the hallway leading to the Manager's Office, break the window and jump out onto the ledge with a Life Seed.
7. In the Manager's Office, open the picture on the wall for a double weapon powerup
8. On the train platform, inside the room with the sign above the door saying "No Admittance", there is a wall that can be blown up, leading to an area with a zombie and 2 cases of TNT.
Episode 1, Mission 3: Phantom Express (6 Secrets+1 Super Secret)
1. In the cargo room, go straight back from the entrance, jump up on the box, turn around and then look up and right. There will be a Life Seed that you can Jump to.
2. Also in the cargo room, jump up on the boxes in the back left corner and open the blue suitcase with the keyhole in it for a beast vision powerup
3. In the dining car, there are two counters, one on the left and one on the right. Each of them has a level behind it, near the floor. Pushing either of these levels will open a small section on the wall behind the counter on the right that contains a reflective shots powerup
4. In the kitchen, one of the ovens opens up to reveal a flare pistol.
5. In the very last room, inside the furnace is a flare pistol, a sawed off shotgun, a tommy gun and a life seed.
6. In the first passenger compartment in the first car, blow open the crack in the wall to tear a huge chunk out of the side of the train. Jump into the new space (gray area), but don't go all the way through into the next compartment. Instead, jump up again to reach an overhead storage area that contains several cultists, a couple zombies, a tommy gun,a sawed off shotgun, a box of flares and 2 bundles of TNT
SUPER SECRET- In the second passenger compartment in the first car, stand in the hole in the side and hang outside a bit. Face the back end of the train (opposite the end where the furnace is) and jump out of the hole, and try to hug the side of the train. You will land on an invisible ledge near the ground. Open up the wall in front of you and enter the super secret area for a sawed off shotgun, a tommy gun, a guns akimbo powerup, a super armor and a life seed.
Episode 1, Mission 4: Dark Carnival (12 Secrets)
1. The train car directly across from the one you start the level in has some fire in the back of it, blocking a hole in the wall. Go through the hole for a box of shells. some TNT bundles and a body armor.
2. Jump into the water at the beginning, swim over toward the right underwater and then surface. There will be a small island under the dock containing a Sawed Off Shotgun, a Tommy Gun, a flare pistol and a Guns Akimbo powerup.
3. At the first Carny game on the left (the one with the moving targets and the cultist), throw a bundle of dynamite into the moving targets and a life seed will appear on the counter for winning the game
4. At the second Carny game, get all 3 zombie heads into the mouth and a message will appear saying "Congratulations, You win a cupie doll!". There will now be an invulnerability powerup inside the mouth.
5. Between the first two Carny games is a wooden fence. Jump it with the jump boots for a beast vision powerup.
6. At the third Carny game, jump inside and start breaking bottles with the pitchfork. After a certain number, you will win the game and be rewarded with an invisibility powerup.
7. To the left of the third Carny game is another high, wooden fence. Jump it with the boots, or jump over it from the manager's office window. On the other side is a drum of bullets for the machine gun.
8. In the freak show, blow up the bars of the cell with the hanging zombie, then go inside and whack the zombie. A panel will open behind you with a Guns Akimbo powerup.
9. In JoJo's arena, activate the warning sign on the front of the tank to open a secret door behind the bank. The area contains 2 boxes of flares, a box of shotgun shells and a special guest appearance.
10. In the ticket booth is a stack of crates. Hit the middle one to reveal a box of flares and a doctor's bag.
11. In the room next to the Punch-O-Meter, there is a stack of boxes in the upper right corner of the room that have scratches on them. Activate the scratches to reveal a backroom containing at least 6 or 7 mimes and a life seed.
12. At the end of the level, after the bridge explodes, jump on the posts left behind. You're trying to get to the gray wall on the other end of the water. Once you get close enough to the wall, blow it open with either TNT or the Napalm Cannon. Swim down into the pool and surface on the other end into an area containing a super armor, a life seed and the exit to the secret level for this episode. The correct combination for the secret exit puzzle is Dagger-Eye-Moon. (The order that the keys were picked up during the level.)
Episode 1, Mission 5: Hallowed Grounds (9 Secrets+1 Super Secret)
1. In the long hallway just after the first gargoyle, turn and blow up the giant picture/design on the back wall to reveal a Doctor's Bag behind it. The item can only be reached by using jump boots.
2. Use the jump boots to jump directly up from the location that boots are picked up to reveal a body armor
3. In the large hall directly before the small room that holds the napalm cannon, there is a small doorway on the right that leads to a pool of water. Swim down, hit the switch to open the path to the right, swim through and surface to find a life seed.
4. In the small hallway with the windows over looking the fountain courtyard, push the strange looking wall and then quickly run up the ramp for an invisibility cloak.
5. In the same room as the Moon key, push the farthest picture to the left to reveal a super armor.
6. On the elevator leading up to the spider key, one of the walls on the way up has a secret compartment containing a body armor. You have to be fast to push into the compartment while the elevator is going up or down.
SUPER SECRET- On the bridge at the end of the level, turn left and look down. You should see a ledge about halfway down. The ledge is also visible on the map. If you try to jump down you to it, you will die, even with 200 armors and 200 health. Instead, stand at point on the bridge closest to the right end of the ledge and jump out against the wall, pressing the open key at the same time. The secret door should open, allowing you to slide inside. The room contains a life seed and a super armor. Press the skull keys on the walls to open the teleporter back to the top of the bridge.
Episode 1, Mission 6: The Great Temple (6+Super Secret)
1. Under the water in the same room as the central wooden platform with the Sawed Off Shotgun and box of shotgun shells is a very small alcove that leads to an invisibility powerup.
2. In the room right after the room with the skull key door, one of the gray pillar/insets in the walls (the one right next to the staircase leading down) is a different color. Push this pillar to reveal a box of shotgun shells.
SUPER SECRET- At the top of the temple, on the same ledge where the moon key is picked up, there is an open air veranda. Go to the middle section and look down to see a layer of clouds at a slightly higher elevation than all the others. Walk slowly off the edge and try to land on the clouds, Follow the cloud ledge around to a door. Enter the door and the message "I can't believe you found this! Here, you can have it all" will appear. The room contains a flare pistol, a sawed off shotgun, a tommy gun, a napalm cannon, a Death Mask powerup, a Guns Akimbo powerup, a invisibility cloak, a Doctor's Bag, a Life Seed and a super armor.
Episode 1, Mission 7: Altar of Stone (Boss Level)
N/A
Episode 1, Mission 8: House of Horrors (Secret Level)
1. In the first area, walk through the wall directly to the right of the House of Horrors building. The wall is an illusion and contains a tommy gun and a drum of bullets.
2. Push the "River Ride of Terror" sign to open a room to the right containing a super armor.
3. In the mini graveyard with the small pool of water in the corner, one of the tombstones is darker than all the others. Push this stone to open the corner wall and reveal a life seed.
4. In the storeroom, the 2 stacks of lumber directly in front of you when you enter the door can be opened to reveal a double gun powerup.
5. In the very last section, after you blow open the crack in the wall, get up onto the sloped edge and run all the way to the end where the wall was blown up. Face the gray wall(right next to you, not the opposite wall) and jump forward to enter an invisible window to a room with six bundles of TNT and a Doctor's Bag.
Thanks in advance to everyone who contributes information to this!

E1M1 Cradle to Grave MISSING SECRETS
10. In the room with furnace, use the saw on the wall and the flaregun ammo will be revealed.
11. In the last room before exit, there is a cover from coffin recline to the wall in the corner and behind it there are flares.
12. SUPER SECRET: In the last room there is a broken wall with a ledge aiming to the end of the level room. From it, you must jump to an invisible secret place located in the wall in front of that ledge, where the napalm launcher is hidden.

Here is a list of cheats for Blood (come on, you know you want them)
Type in "T", cheat code and then enter.
I WANNA BE LIKE KEVIN - God mode.
MPKFA - God mode.
NOCAPINMYASS - God mode.
VOORHEES - God mode.
CAPINMYASS -God mode off.
IDAHO - Full weapons.
MONTANA - Full weapons and items.
LARA CROFT - All guns and unlimited ammo.
BUNZ - Akimbo guns.
KEYMASTER - Full keys.
SATCHEL - Full items.
GRISWOLD - 200 armor.
SPORK - 200 health.
COUSTEAU - 200 health and diving suit.
MARIO - Level warp.
CALGON - Level warp.
ONERING -Invisibility.
EVA GALLI - No clipping.
RATE - The frame rate.
GOONIES - Displays the whole map.
KEVORKIAN - Suicide.
FUNKY SHOES - Boots.
MCGEE - Light yourself on fire.
KRUEGER - Light yourself on fire with 200 health.
JOJO - Drunk.
I love that the no clipping or "GHost" mode is Eva Galli....

Any Blood walkthroughs out there?
I am sucking at trying to get very far into the game (at the train station, phantom 666).
Cant find a walkthrough.
:(

There's one here.
http://www.neoseeker.com/resourcelink.html?rlid=73940&rid=68344

Episode 1, Mission 2: Wrong Side of the Tracks
1. In the Train station, in the same payphone bank as the ringing phone, one of the phones slides down to reveal a basic armor
If I remind well, if you stay over the telephone while it's down you can also get on the top of the phones and take a flare

Yeah, but it isn't one of the "secrets" of the level. Its just an item that sitting there. Please try to keep the addition of posts to posting secret locations. Also, keep in mind that I'm probably missing a least a few secrets on each level. I want this to be a complete resource for people to use, but I also want to progress in the game, so I only spend a certain amount of time in a level after it ends attempting to find any secrets I may have missed before I move on to the next one. I hope everyone finds this thread useful, it is going to be more work than I thought for me to complete it, but I'll gladly do it if it helps people.

Well, that takes care of Episode 1, now I'll start on Episode 2. According to level ending stats, I didn't miss very many of the overall secrets for this episode. I missed 3 in E1M5 and 4 in E1M6, so if anyone finds those, just post them there. Thanks!
Episode 2, Mission 1: Shipwrecked (5 Secrets)
1. Before jumping onto the ship, walk around the giant iceberg sticking out of the side of the boat. Between the ice and the side of the ship is a diving suit.
2. After jumping onto the ship, look off to the left to see a dark cave that contains a Voodoo Doll.
3. In the Cargo Hold, where the fire key is, there is a Doctor's Bag hidden behind one of the stacks of crates.
4. Underneath the boat, far under the water and ice, is a cave containing a small passage to the right that holds a life seed.
5. In the underwater room that holds the Skull Key, there is an alcove the right corner that holds a life seed and a super armor.
Episode 2, Mission 2: The Lumber Mill (2 Secrets)
1. Climb up the stacks of lumber in the main yard. High up, near the left wall, is a window. Jump through for flares, tnt bundles and a few spiders.
2. In the start of the level. climb the lumber stacks, break the window and jump through to a room with a cupboard. Push the cupboard for tnt bundles and a super armor.
Episode 2. Mission 3: Rest for the Wicked (5 Secrets)
1. When walking into the area with the center structure with 2 switches inside, turn left. The hedge in the corner will be a different color. Open the hedge for a body armor.
2. The small house with the Bloated Zombie and the skull key has a hole in the ceiling. Jump using the boots to get on the roof and collect some proximity detonators.
3. Behind the house mentioned above is a garden shed with some bloody tools inside. Go inside this shed and push the left wall for a doctor's bag.
4. Jump into the swimming pool using the diving board, turn around underwater to see an opening containing a life seed.
5. Facing the door into the bath house, walk around to the right of the house and you will arrive in a small yard with a shovel sticking out of the snow. Use the shovel and the hedge in front of you will slide down, revealing a frozen person who can be shattered for a Death Mask powerup
Episode 2, Mission 4: The Overlooked Hotel (Holy Shit, 17 Secrets!)
1. In the hedge maze, there is a small elevator that will take you to the top of the hedge. Once on top, look around and you will see a box of flares on the next hedge over. Jump to that hedge to collect the flares.
2. Before you enter the hotel, go back to the top of the stairs that lead down into the courtyard where the entrance to the hotel is and hop up on the ledge that circles around the courtyard. Walk around to the right, push the first gargoyle statue off with the pitchfork so you can get past (it won't wake up), then move toward the large pillar next to the entrance where another gargoyle statue sits (be careful, this one will wake up). After the gargoyle has been dealt with, look across and you will see another gargoyle on the opposite pillar with a body armor floating next to it. Get a running start and jump across to collect the armor.
3. Upon entering the hotel, go past the staircase on the left into a small alcove and there will be a brown wall panel with a cross on it. Open this panel to enter a room with a box of shotgun shells and a case of tnt
4. In the hallway at the top of the first staircase on the right is a picture of some intestines. Push this picture to slide down the wall behind you and reveal a body armor, a drum of bullets, a box of TNT and a buttload of spiders.
5. One door down from the fire key door is a bedroom. The closet on the right side of the room can be opened for a fire armor.
6. In the same room, the bookshelf on the left side of the room slides open to reveal one of the 5 tomes that must be collected to open the entrance to the secret level for this episode.
7. Stepping outside the bedroom mentioned above, there is a grandfather clock at the end of the hallway. Use the clock to reveal a secret passageway
8. Following this passageway to the left leads to a voodoo doll. Additionally, jump through the small window into a bathroom, and search the adjoining bedroom for the dagger key and the 2nd of the 5 tomes.
9. Following the passageway to right leads to a door with a design that looks like a skull with blood running out of eyes. Open the door and enter the room for an invisibility powerup, and the 3rd of 5 tomes on the table.
10. Continue on following the passage to the end, open the end panel to reveal a teleporter
11. Enter the teleporter and find 2 cans of napalm ammo on the other side.
12. Go back to where the grandfather clock and continue on down the hall. The first door on the left is a bedroom. Walk across the bed to open a secret passageway above the headboard.
13. Continue on down the hallway. One of the walls on left will be different colored. Open it to enter a library. One of the bookshelves in this first room acts like an elevator to the top of the shelf where you will find the 4th tome.
14. In the second section of the same library, use the jump boots to reach the top of one of the shelves for 2 cans of napalm ammo.
15. Use the boots on the shelf against the opposite wall for a guns akimbo, then follow the shelf along into a secret room for a drum of bullets, a box of flares and a box of shotgun shells
16. In the room with the moon key, enter the fireplace and jump up into the small secret area for a guns akimbo, a voodoo doll, a box of shells, and a case of tnt. Also note in the moon key room, the black triangles on the floor. Those triangles represent how many of the tomes you've picked up. Remember that, when you get the last tome, this is where the portal to the secret level will appear. (The portal will look like a cloud of smoke in the middle of the 5 black triangles, just walk into the cloud to exit to the secret level).
17. In the room with the spider key, open the bookshelf in the corner for 3 cans of aerosol, a case of tnt and a doctor's bag. Also, the final tome is in the same room as the spider key.
Episode 2, Mission 5: The Haunting (8 Secrets+1 Super Secret)
1. Right after entering the mansion, follow the left path around, between the bookshelves until the path dead ends at a small library with green walls and a single window. The bookshelf in the corner can be opened for a box of shells and an invisibility cloak.
2. In the room with the fireplace that has 2 pieces of wood crossed in front of it in the shape of an X, one of the bookshelves can be opened for a guns akimbo.
3. In the main library, there is a fireplace. The fire will not hurt you and the back wall can be opened for a fire armor.
4. Facing the front door of the house in the start of the level, use jump boots to hop over the hedge on the right of the house to get a beast vision. This can also be reached by jumping out of the upstairs window, out onto the hedge and then down to the ground.
Episode 2, Mission 6: The Cold Rush (5 Secrets)
1. There is a large ice cliff near the start of the level. If you look out into the distance, you will see two massive ice columns. One of them has a life seed sitting on it. Getting running starts and carefully jump to the first column, then to the one with the life seed.
2. After getting the life seed, jump to the next platform, walk into the small passage and look to the left of the hole to see 4 shotgun shells and 15 bullets sitting on a small ledge that you can jump to.
3. Inside the door directly opposite the first skull key door is a tower with 2 ledges in the ceiling. Use the jump boots to get on the ledges and collect 2 proximity detonators and 3 remote detonators.
Episode 2, Mission 7: Bowels of the Earth (2 Secrets)
1. After making the huge jump across the chasm at the end of the mine car ride, head to the the right to find a narrow path that opens into a small room that holds a life seed.
2. After going underwater, swim into the left passage to find the large wooden level that must be pushed to open the way forward, but after pushing the lever, check out the right side passage for a new opening that surfaces into a small room containing a diving suit, a drum of bullets and a box of shells.
Episode 2, Mission 8: The Lair of Shial (Boss Level)
N/A
Episode 2, Mission 9: Thin Ice (Secret Level)(2 Secrets)
1. From the start, swim the under the water and the far forward under the ice for a doctor's bag and a super armor.
2. In the 3rd ice field, when the ice cracks, swim down and to left to find a small niche in the wall with a drum of bullets and a box of shells.

Overlooked Hotel has a load of secrets, I somehow managed to get 18 out of 17 (according to the score screen).

According to a Blood wiki page that I've been using as a semi-guide, it actually has 19. Even though the score screen only lists 17, there are actually 19 places in the level that count as secrets. When I finished the level a little while ago, I only had 17/17, so I must not have found the extra 2 places. What I've been doing is I play with the Blood wiki page and this thread open, so each time I find a secret, I minimize the game and post it right away, then when I come to the exit of a level, I go run back through and see if I missed any. I keep the page of the wiki at the top until I finish the level, just so I can list the total amount of secrets here before I start the level, I don't read the secrets section until after I leave the level.
EDIT- Just found a weird bug in E2M5. The spider key is located between 2 sleeping gargoyles that don't wake up until the key is collected, but the moment you pick up the key, there will instantly be 3 gargoyles there, even though there were only 2 statues. One of them must have a conjoined twin, lol

They're all really easy to find though, in other levels I can go without finding a single secret.

Yeah, I got 17 of 17 and I didn't even read the secrets section on the wiki page for that level. Some of them are just opening different doors to the central secret passageway that runs inside the level. Or opening a panel to a teleport would be one secret, then walking through it and getting the items on the other side are a totally separate secret, lol. Some of the levels are really hard to find secrets for. I have 4 of the keys so far for E2M5 and I haven't found one goddamn secret yet, lol

Talking about bugs, in E2M7: Bowels of the Earth, when the mine cart stops due to a rock in the way, trying to walk between the cart and the left wall causes you to die instantly (sometimes you just stop like normal but if you keep forcing it, it'll happen eventually).
A big wtf moment when that happened to me.

I wonder if thats the same glitch that causes insta-death sometimes if you open a cabinet door and it touches you while its opening, Thats happened to me a number of times. Especially frustrating if you haven't saved in awhile ;\ It also happened to me 2 or 3 times in E2M9, the secret level. I'd be in the water, trying to jump back onto the ice and I would touch the ice while I was jumping and just die for no reason.

Alright then, time for Episode 3. Have to say, this guide is turning out better than I expected.
Episode 3, Mission 1: Ghost Town (10 Secrets+1 Super Secret)
1. In the first building you can enter, in the back of the building there are lots of pictures hanging on the walls. On the right side, there is a picture of a woman holding a child that changes images if you look at it long enough. This picture can be opened for a drum of bullets and two dynamite bundles.