From the back cover:
Enter the World's Most Legendary Dungeon: From the nefarious black skeletons to the lair of the arch-lich Zelkor, Rappan Athuk is the most famous and feared dungeon in all the lands. Do you seek the mithril gates? Or perhaps the ring of the sorcerer Akbeth? Does your quest take you to Hell itself? Then you have come to the right place. A pity you wont be staying long.
Death and Despair: The first in the R series of D20 dungeon modules by Necromancer Games, Rappan Athuk 1: The Upper Levels is the grand-daddy of all dungeon crawls! These caverns, passages, traps and hidden chambers defy even the most experienced adventurers. Rappan Athuk 1 features six levels of this infamous multi-level dungeon, including monsters your characters have never imagined in their worst nightmares. Need a new dungeon to go with those dragons? Rappan Athuk awaits!