Underdark

The Underdark, as named by the Arcane Delvers, its initial discoverers, was a massive, weaving catacomb of tunnels that lie beneath the lands of the Dwarves in Anthos. Originally, the Arcane Delvers used it as a source of sandstone, as pockets of the materiel were common there, though they soon realized how large, and dangerous, these tunnels were. The only known entrance is nearby the Adunian city of Brom'Kah, inside the abandoned Arcane Delvers tower. Few people in Anthos know its existence, in fact, most being Delvers, and as such the area has been rumored to have been used for a Necromancer's hideout, or even, something more sinister. With extensive mapping by the Delvers and other sources, the tunnels can be tracked going all the way to Vaerhaven, and there would seem to be a hole in the roof of one of the tunnels, directly under where the Mages college is estimated to be, though such hasn't been extensively explored or confirmed.