New screenshot from Teemu:
It's a cave. But, there is something different in this cave. It's not just any cave, it's there for a reason. The inhabitants of the cave made it like that. It's a functional cave and a real part of the game world. This small difference made me think "why, of course..." If you create a random level with random monsters that has no other function than be a level, it's going to be poor.
A new feature is unexplored tiles shown in dark grey color. It makes navigating easier when you see what areas you have visited and makes a clear distinction between floors and walls that are obstructed by the field of vision.