Realms Lore - History of the Bell in the Depths
The power of Northkeep made it an obvious target for orcs, giants, and other evil races. However, these creatures were not inclined towards sea actions, and Northkeep seemed safe until the day when (according to legend) 40,000 inhuman mages, shamans, witch doctors, and priests of all foul races gathered on the northern shore of the Moonsea and began to chant, bringing the vengeance of their gods down upon the human interlopers. The gods (at least some of them) came and destroyed their priests for disturbing them, but also sank Northkeep beneath the waves.
The upper reaches of Northkeep-its slender, now-broken spires-can be seen beneath the water by boats that sail nearby. This is not attempted often, however, as the region is said to be haunted by the original defenders of Northkeep, seeking company in their watch over the Cold Lands. On fog-ridden nights the bells of the tallest towers, despite being submerged, can be heard as far away as Hillsfar.