Dungeons. Skeletons of majority of OSR games.
Having a prepared dungeon is everything you need to run at least one game. Having a GOOD, detailed dungeon, filled with treasures, strange creatures and wandering monsters can suffice to keep your group entertained for weeks.
As always with my "Elegant Fantasy" series, you roll for inspiration, not stats. If we’re both lucky, then this book will inspire you, and help you create a fun adventure for your players, one that they will remember for a long time.