Archeology has answered a lot of the mysteries of our past. But while it has shed some light on what our history looked like, it also unraveled a lot of unanswered questions. Many of the archeological structures around the world are shrouded in mystery and their story is mostly unknown.

Let’s uncover the secrets of some of the most puzzling archeological structures on the planet.

From the Mystery of the Chinese Emperor’s Mausoleum to the Shell Grotto, nobody knows who built these structures.