Grimrock

Is it possible to break some walls? Are there any fake walls? I am in the crystal mines in the north-west room (crystal mine abyss) and it really looks like a wall that could be broken...

I don't know the answer to your question. But there is a pickaxe in the game.

no on the walls.
unless I missed something and I am fairly thorough.

the pickaxe threw me off too so I tried a lot especially in mines. Unsure why they placed that there. Unless you run right to it early on with light weapons

Doesn't appear to be. At first I thought that you might be able to do something because some things will give a "miss" result when hitting it (like when you whiff on air), and others won't, but that appears to be unrelated to anything meaningful.