An ovoo (Mongolian:овоо, Traditional Mongol: ᠥᠪᠥᠭᠭᠠ, heap) is a sacred cairn found in Mongolian shamanic religious traditions, usually made from rocks with wood or from wood. Ovoos are often found at the top of mountains and in high places, like mountain passes. They serve mainly as Tengriism religious sites, used in worship of the mountains and the sky as well as in Buddhist or Shamanist ceremonies, but often are also landmarks. Almost all researchers say that originally all ovoo were made from holy woods, and to this day they must include wood elements inside of them.