Cut inside the mountain, outside of the Clan's territory is the Black Tunnel. The home of the evil, banished, and just plain unwanted cats. They usually have some issues with the Clans and are known to be violent, if they aren't they tend to be classified as spineless loners by these cats. Darkness reigns in the Tunnel that supposedly goes all the way through the mountain. No one has ever gone the whole way though, that or they have legends about cats trying only to go mad in the darkness. You'd have to be one crazy cat to attempt it in the first place and if you weren't already you would be when you got to the other side.
