From publisher blurb: Behind the walls of the caravansary, guarded by professionals, you can finally relax a bit. The Inn is reputed to have training facilities for warriors, fine food, and soft beds. All are welcome… And nearby are rumored to be hidden secrets of the ancients along with valuable treasures. Hidden Knowledge can be used as an adventure in any campaign world, or played as a sandbox in Hellebarde's default setting. Written and tested with Castles and Crusades RPG, notes are provided for conversion to other OSR systems. Forbidden Knowledge can be used stand-alone or as part of the Exterris Adventure Tome AT-5 (AT-5 plus ONA-17 through ONA-20).