Dark sun that isn't actually dark sun.
The Tower of Bondsmagi
An organisation created by an ever-increasing series of powerful mages knocking at the doors of less powerful mages and asking if they’d like to join their new club, or die.
The source of a number of antagonists, most notably Sheraptus and, indirectly, Gus-as-Dragon (via a ludicrously powerful potion of dragon form). Slightly demolished and de-arch-maged by Gus before The Competent Adventurers threw a whole lot more equally powerful potions in his general direction.
Scrying has revealed that Sheraptus phylactery is here, kept by what is presumably a senior mage.
SIXTY YEARS ON
The wizard tower survived one of the blasts from Vecna’s sun, when the second hit, most of the wizards had scattered to locations unknown, many hundreds of promising students were killed in the second attack.