Grimrock

I'm stuck on level 3 , in the "this path is best for dungeon explorers" area. I have the green gem that the hint tells me how to find, but I cant find the other green gem. What am I missing?

Ah, cool. I'll have another look around. Thanks for your replies.

I have already opened the door, and gone into the alcove. However, there is no way to go beyond that, because I have not yet been to the other two pressure plates, and there is no way back. Edit: I went to one of the other pressure plates, past the snakes corridor. I think I had a key unused from ea...

I seem to be stuck in level 9. I got past the sanctum with the three altars, found the lightning blade, but there seems to be no way forward (The central area didnt open when I reached it) and no way back (the door to the sanctum locked behind me.)

Am I missing something, or have I hit a bug?