Garamantean Gothic
So, have you heard of the Garamantes? If not, google them right away. Or read The Fate Of Africa. I found out about them through the latter. I heard the part about extensive underground water-mining operations and my mind lit up with a big neon sign saying "DUNGEON". Plus, the whole concept of a cosmopolitan urban society being able to exist in the middle of a desert without extensive magic is pretty cool.