Kalidnay was once a large walled city home to Kalid-Ma the Sorcerer-King and High priestess Thakok-An. Thakok-An attempted to ascend her king into a Dragon using the life energies of the city's populace. This, however, ended up putting the king into a comatose state and uprooting the city through to the Shadowfell (Demiplane of Dread) (Ravenloft setting).
It exists as a ruin in Dark Sun, populated by various tribes and dangerous creatures.
Kalak of Tyr, believed to have slain Kalid-Ma ended up trying to repeat the process of ascension also trying to kill the populace (See Tyr).
There is a large discrepancy that Kalid-Ma and Thakok-An switched genders during this transition in the Ravenloft setting, however this was due to the writers of Ravenloft not having to pay royalties to 'Wizards of the Coast' in doing so. For roleplaying intents and purposes; it should be looked at as always being Kalid-Ma as the male, due to the fact the city's name is KALIDnay and not THAKOKnay.