The Diving Bells of Oagon
The flooded ruin of Oagon, a lost city of Lirgen at the mouth of the Black Flow, provides a frequent destination for explorers. In particular, Oagon was reputed to be the host of the famed magical vaults of the Hundred Halberd Consortium, a once-opulent but now vanished merchant company that dealt in both magic items and exotic creatures. To access the sunken streets, explorers from Avistan and the Knights of Salvation constructed a series of giant diving bells. The cables that lower the thick glass bells permit expedition teams to slowly descend to the ground and explore the flooded streets below. The bells are far from safe, however, and accidents are common. Worse, there are recent reports of slender, long-tailed aquatic creatures that snatch divers and then disappear in the maze of underwater streets.
Sources: Pathfinder Chronicles Campaign Setting