Image: Inside the Bunker of Hellfire Corner, in the Cliffs of Dover, Great Britain.

Subterranea are any kind of artificial underground sights. Maybe you think there is no good reason to dig a hole, instead of the search for valuable ores. But man used caves for many purposes, for living, storing food and worshipping. And if the geology of an area did not provide natural caves, man often built artificial caves as he needed them.

This chapter subterranea contains some explanations on man made underground structures. Although mines belong also to the subterranea, they are such a wide and complex field, so they have their own chapter. Subterranea - as defined here - are all kinds of artificial cavities except mines.