The Ruins of Castle Gygar is a 360+ room megadungeon designed for old school tabletop RPGs. It is designed with Old-School Essentials in mind but will play great with any OSR B/X compatible game, your favourite retroclone, five-ee, or fantasy heartbreaker.
This is a companion discussion topic for the original entry at https://rpg-trader.com/products/4346/the-ruins-of-castle-gygar