The northern mines are an abandoned mine system, left by humans long ago. The mines are reasonably stable, but are collapsed in some areas. It is easy to get lost as they span for miles and miles. You can find various bunkers, containing things left behind by the miners that used to work there, such as helmets, torches, and long extinguished fires. But if you do go in too far, there is no food, water or heat, so it is a dangerous place to get lost in.
↣
Schizophrenic Fever Dreams