Grimrock

So I think I'm done in level 10.

Go and use the prison key? I'm assuming that door you can't open is a secret - if you want a hint check the spoiler

I don't know where to use the key. And it's not an iron door. In one room, there is a hole in the ground so you obviously can't get over, but there is a door, but no mechanism to open it.

Ah, I think i see.
Regarding the door - is it the one that you can see stairs behind it? - have you tried jumping?

Prison keyhole is downstairs

Thanks. Got over that place now.

Where "downstairs" is it?

go explore, you will facepalm when you see just how easy it is to find....

I've been searching. I honestly can't find it. I've been in the huge room with all the pits, put markers on the map and compared the location on each floor to try falling inside a room which is blocked off by a gate but no success...

Edit: Oh my god...I noticed those stairs near the crystal earlier, but since I had been there earlier I thought I had already checked that place. Geez...Indeed..*facepalm*....Thanks though man.

told you :p

also, you haven't checked all the pits if you didn't get in that room