Sargauth Enclave

The Sargauth Enclave is the name some use for the Netherese outpost on the third level of the Undermountain, but the actual name of this place has been lost over time. It was created c. by an order of powerful wizards from Netheril to serve as a safe haven for conducting magical experiments, but after a decade it had grown into a city of about one square mile (2.6 sq km). The River Sargauth flowed through this magical place and it was the only route to the outside world, through the South Seacaves.

Downfall
When archmage Karsus caused the fall of Netheril in, there was a powerful surge of magic into the Sargauth Enclave. The enormously high ceilings of its caverns were supported by magical means instead of columns or pillars and the disruption of this magic caused a collapse which destroyed and engulfed about two thirds of the enclave's structures. Anything left uncovered was vaporized, but the skulls of thirteen of the wizards would survive, magically transformed into the Skulls of Skullport.