ie, without having seen/heard about it before.

Two that come to mind: Bio Menace's Apogee room and Warcraft 3's Hydralisk. The Bio Menace one was pretty easy to discover since it was behind a locked door in one level that, along with the key, was hard to miss. The Warcraft 3 one on the other hand is well hidden, and you actively have to try to explore every corner of the map to find it. Which is a good thing to do on every level, since Warcraft 3 has tons of secrets. It was quite useful to finish the level too, though not as OP as I would've hoped. Hopefully one day they'll hide an Ultralisk somewhere in Warcratt 4!

I think we'll sooner see the Zerg as a playable race in World of Warcraft, than a new Warcraft RTS.

On topic- I think I found the Star Trek episode in Max Payne without reading about it before. There was a lightsabre in Republic Commando (not a usable one sadly), but I'm not sure if that was an easter egg (if it was hidden I mean, I just can't remember). ANd there was Millenium Falcon in Jedi Knight: Mysteries of the Sith. In fact, I think there might have been two, witch confused me a lot.

I remember discovering Top Gear 2's password into any level cheat by accident all by myself. I genuinely thought it was a bug, not a legit cheat. Only after I saw it on a magazine, years later, that I became aware that it was an intentional cheat.

When I played RAGE, found some easter eggs that were fun on their own, some that I did not even recognize and a few that blew my mind off. Those coolest ones were (link are to RAGE wiki, may contain spoilers):
- The Quake room
- The Doom room
- The Developer Graffiti room

After finding these rooms and nearly finishing the game, I Googled for more easter eggs and thus, went to find The Wolfenstein room, which was also very cool. All rooms (except Dev Graffiti) represented how the world of each of those games actually looked like. Playing in RAGE wastelands, finding these rooms were extremely mind blowing.

I found the Chris Houlihan room in Link to the Past all on my own, in pre-internet days too.

Yeah, pretty much :(

Playing Wizardry Gaiden 3. If you step in a certain spot in the bonus dungeon, you get the message

P.S. TREBOR SUX

Easy to find when you reach that point, but I thought that was an interesting, though minor, easter egg.

(Also, Murphy's Ghost can be found early, but I didn't find it on my own.)

I found the hidden sign in GTA III by accident. Quite fun.

Here's an interesting one that I knew about beforehand, but happened to trigger without intending to.

In Breath of Fire, there is one point where the same message appears again until you cancel it. If you read it a certain number of times and then cancel (I think it's something like 3, but I could be wrong), you get a glimpse of a Street Fighter character.

Well, I happen to reach that point, see the event (I believe this is optional), and cancel out after just the right number of times and see the easter egg.

Another one, which I did find on my own:

Tombs and Treasure (NES) has a sound test, which I triggered by accident and was not able to reproduce.

Edit: Another one: I found the sound test in Defenders of Oasis (Press Up + Start), and was able to remember it. I knew that I wanted to go up when loading the game, so I was holding up when pressing start to get past the title screen, and that triggered the sound test.

Speaking of sound tests, I was dumbfounded when a found this hidden track on Incoming's CD when I decided to put in a CD-player:
https://www.youtube.com/watch?v=h4-DmFSrY4w&feature=youtu.be&t=1835
I still wonder if there is something you can do ingame to trigger a sequence with that music. Perhaps it was in the credits somewhere and I just missed it.

I found out Bruce Wane is Batman all by my self

Oh come on!