Rob's Greyhawk Undying Wyrms
One of three places where the Sword of Orcus , Helring,could be destroyed, and in fact the one which served that purpose. Also the location of a great evil which the shade of Sir Redgarth wishes destroyed.
This castle is one of a number of strongholds owned by the family Strahd,one of the leading Vampire families, and contains at least 2 locations where all 13 families can meet; one a normal looking boardroom whose exits lead to distant locations, possibly on other planes, and the other a more ceremonial location with a ziggurat atop which is a trapped monstrous demigod.
Hidden in the keep is a chamber sacred to Pelor, where good people may hide and rest during their explorations.
Prisoners in the keep rescued by the party include one of the grandchildren of the Elven High Queen, return of whom to the safety of the Church of the Moon at Innspa earned those who performed that service a considerable degree of kudos in elven eyes.