User blog comment:Blanzer/Suggestions/@comment-2.101.9.215-20110902194214

Imagine a layer behind walls where you could build extra rooms and have a secret place to dwell and store your stuff! A safe place where players can't see and enemies can't spawn (except for maybe being able to access it through the same way as you).

Of course, in such a layer it would be totally unnecessary to have naturally occurring tunnels and stuff (except for maybe in dungeons), and it would be purely for extra building space and rooms not visible from the normal front layer.

Also, you have to place brick walls in the front layer to form the back layer, otherwise you could just tunnel around in a totally safe, hassle-free, game-ruining way. also, you can only place and destroy doors on the back layer from the outside, and it doesn't work on dungeon walls.

With this feature you could have background houses so that they are not totally always in the way, and a greater sense of privacy.