I played at this game for some hours, but now I really can't find a way to proceed. I solved some quest, like the one of the deserter guard, and i explored all the surroundings, including the various caves.
I know that the baroness is implied in the murder of the merchant, but i can't find the baroness, i can only arrest Master D'Arvais, but I couldn't even find the heretics he spoke about and he doesn't say anything if I arrest and torture him.
What I have to do?

If you want to find the baroness, you might want to take a look at the iron mines. She might be around... Or under.

Thank you, i'll take a second look at the place. :D

EDIT: The "magic" portal in the orc camp, just outside the mines, does not work or it's some kind of bug?

It only works when activated from the other side (and I'm unsure right now if it's two-way even after that)

I'm crawling the mines right now... But I'm so disgusted with poison.. It lasts around 5 minutes!! 5 minutes of losing hp. That's just horrible. So many potions, so much gold lost.. God really has forsaken this land.

Oh yes. I got poisoned down there just as my NPC party member used my last health potion. After realizing I couldn't make it back to town alive, I desperately tore apart barrels to find a health potion. Luckily I made it back with 5 HP to spare.

Tell if you find out what to do, I'm completely stumped about how to get through the giant double doors.

This is a complete map of the first floor. Look at it - see the stairs down in the lower right corner? Get down there. You can find a key on that floor that unlocks a locked door on it and behind those, there's another key that finally gets you trough the door you mention. Thak Cervic for details.

Thanks!

Is it in a chest on the second floor? Because I can't open those.

Attack it until it opens.

After hours of meaningless searches for keys, i found out that doors and chests can be opened with the force, or even fireballs. Unfortunately, a door can bear more than 200-300 damages, so it's a long and boring procedure.
There is also a spell thath opens chests and doors that are not magically sealed.

I'm stuck at the bridge now, I have tried bashing chests open, but one of them insta-kills my party, so if there's anything of use in there for me, I can't get it

Try using ranged weapons / magic to bash it. You can do that from distance, so the spell doesn't affect you.

I tried it aaand it works, it's two-way then! Oh my I'm so happy now! I needed the portal to escape because all my bows are broken ~.~ so I wasn't able to fight anymore. But now I have just a short way back to town and after that I can just use the portal instead of walking through the whole damn mine.

How do you pass on the other side of the collapsed bridge WITHOUT levitation?

I made the lower levels... but i see no road. Please. Help.

Someone know where to find the heart of the vampire bishop? And where is the paladin commander sword?

Thank you, really, for your answers.