An oubliette is a type of dungeon or prison cell that is designed to hold captives in complete isolation. The term originates from the French word "oublier," meaning "to forget." These cells are often deep underground and have a narrow opening, making escape nearly impossible. Historically, oubliettes were used in castles and fortifications during the medieval period. The design of an oubliette typically includes a vertical shaft or pit, where prisoners could be dropped and left without any means of escape. This method of imprisonment was not only a way to confine individuals but also served as a psychological punishment, as captives were often forgotten by their captors.