Skullport

Skullport
Also known as the Port of Shadows, was a teeming hive of evil lying deep beneath Waterdeep on the third underground level of Undermountain.  A mile and a half beneath the orderly streets of Waterdeep squats the most wretched and lawless pits of thieves, buccaneers, slavers, and sellswords the Realms has to offer. Under a moldering tangle of catwalks threaded between the stalactites and stalagmites of the cavern city, illithids, drow, beholders, and others plot and trade with emissaries from the surface. Monsters prowl the dark recesses and alleyways, gangs of zombies shamble about performing menial labor, and anything and everything can be bought and sold: lethal poisons, foul tomes of forbidden magic, and slaves.

The only law is meted out by the enigmatic Skulls of Skullport, mysterious floating humanoid skulls whose capricious judgments and madness-induced destructiveness are the stuff of grisly travelers' tales. Gold rules the ever-present twilight, and only those with keen eyes and blades may keep it long.

Mystic Obscura in Skullport
Travelling in Skullport, Mystic Obscura stopped at an Inn mainly for Orcs, while searching for Drada, they also found evidence of Aegon's brother; Agronak, in the city, and split up to find them.

Eventually, they found Drada, who in turn led them to Garhan, Agronak's lieutenant. The group then moved on to Dissumusk's home, where they searched for an artifact of great power. Upon their encounter with Dissumusk, they left Skullport and returned to Waterdeep, with Drada's head in a bag as payment.

The group eventually returned to face Dissumusk, who had taken their friends and family. Aegon died in the resulting fight, for the second time, but they eventually slayed the Mind Flayer, once and for all. They then headed to a secret location within Skullport, to face Xanathar.