Grimrock

I'd like to make a hallway directly adjacent to a room, but at default that just breaks down the walls and makes it a large open space. I can't seem to put walls in place either, using say dungeon_wall_dirt_1 and then expanding the area behind the corridor, as that just removes the walls.

Is there a way to have corridors adjacent to rooms?

Use the dungeon secret door and put pillars between them.

Yes, that will work, and you can just never have the secret door open.

I wonder if you did this all over the place all throughout a level if it would cause problems, maybe screw with monster path-finding or engine performance in some way

Komag wrote:I wonder if you did this all over the place all throughout a level if it would cause problems, maybe screw with monster path-finding or engine performance in some way

It should work OK. One thing is though that monsters have a tendency to wait behind a door if the player is right on the other side of it, on the adjacent square, but since the player wouldn't actually see this happening, I don't think it would be much of an issue. Otherwise it should be completely fine regarding AI, performance and so on. I think.