History
A maze of underwater caverns carved by underground rivers. Known for it's escaping undersea gases and located with in the Bermuda Triangle.[1]
The Atlantean criminal Zoga was exiled here and the gases mutated him and several sharks, that he then kept as pets. He spent years learning which parts where safe and which where dangerous. Eventually he and his partner Ruthar started using it as a base of operations for an group of surface and Atlantean criminals that preyed on surface shipping in the region. Namor blew up the portion they were using as a base after he stubbled upon their operation and defeated them.[1]