Abandoned Prison for the Mystically Insane

From the introduction:

From the surface, this area looks nothing like nothing more than a small hilltop, raised slightly from the surrounding area. On the North side of this hill however, a small cave leads into a cave complex which holds a deep, dark secret – this site was once used to house witches and wizards who had gone mad with their magical powers and committed terrible crimes against humanity. The lower levels, incased entirely in Iron, prevent almost any attempt at escape. Some have come close, but failed to actually reach the light of day; now the prison and caverns are long abandoned by the wardens who formerly guarded over them. The condemned have gone long insane, often driven into undeath with their madness.