Picture being in a dark, narrow chamber, kind of like a dungeon, but with a twist. An oubliette is a special type of dungeon that's designed with a trap door at the top as the only entrance or exit. Back in the day, if someone got tossed into one of these, climbing out wasn't an option. They were pretty much forgotten, hence the name "oubliette," which comes from the French word "oublier," meaning "to forget."