I never saw this kind of wall bug, but maybe others did.
Concerning the in between world: Speak to Raze, Kiya or TheMightyOne. They (and others) have experimented with it. There is an entrance in the Dwarfen mine and one through Verdistis gate, or you can hex yourself there.
The house in Dwarfen forest can not be reached on normal way. However you can hex yourself there or get there by pyramid hopping. (throwing pyramids and teleporting). It is not worth doing though. You can´t move in these areas except for teleporting and there is actually nothing which is wotrth visiting.