Mysterious Dungeons
Mysterious Dungeons are traditionally multi-floor dungeons wherein the floors themselves are small and randomly generated. Here is a link to a floor generator, and below is an image showing the settings I use to create Mysterious Dungeon Floors. So long as everyone has a character, a session of Mysterious Creatures and Mysterious Dungeons can be easy to set up and play in very little time. Feel free to make your own custom dungeons instead.