Kaalinth

Kaalinth was a small coastal fortress and small city, home of the inventor of the Calendar of Harptos, long-vanished by the 14 century DR.

Description
The stone walls of the fortress-keep of Kaalinth hid a small city. The structure was a sprawling castle with a single massive tower.

Kaalint's exact location was debated among sages, but most agreed that the keep stood either on Amn's or most likely Tethyr's territories. The true location was north off the coast of Velen, around two-thirds length of Tethyr Peninsula, along the area known as the Dragon's Neck Peninsula.

History
Most of the keep's history was considered to be lost to time. However, Kaalinth's fall and subsequent fate were known to some sages. The keep's tower was blasted by an angry dragon who took the town's ruins as its lair. Later, a cabal of dragon-riding mages defeated the wyrm, but the battle ruined the rest of Kaalinth. Eventually, the land underneath the ruins collapsed into a massive cave, part of the Underdark after a powerful spell was unleashed within the caves. The area was weakened, permeated by numerous passages into the underground realm used by smugglers, and collapse was imminent. What was left of Kaalinth was considered a dungeon by those of adventuring mindset. The ruins' topmost part could be accessed from underwater just offshore of the castle's previous location.