Underport: Abyssal Descent, a vintage mega-dungeon nearly 4 decades in the making and compatable with Knights of the All Mind and other OSR/d20 rule sets. Originally written incrementally during RPG's early years between mid-1978 and late 1981, the style was swords & sorcery focused on heavy fighting action.
Now there are more than 250 individual, detailed encounters on 9+ dungeon levels plus a small pirate village and 2 underground keeps. Levels of difficulty range from 1st to perhaps 16th or 17th for a party of 5 or more adventurers. However, these are not "game balanced" encounters and players must measure when to cut & run. Revel in the chaos with an artifact based from the Wild West era of The World's Most Popular Role Playing Game!