Ovoo (in Mongolian "heap") is a cairn made in Mongolia for ritual purposes. They are made from stones or wood. They can be usually found on mountains. People passing by an ovoo traditionally circle around it three times in clockwise direction. A person makes an offering by adding a stone to the pile. Some people leave money, milk or some alcoholic beverage. He or she then makes a wish.
Ovoos are part of traditional mountain and sky worshipping rituals. These rituals are held at the end of summer. During ritual a person puts a branch on the oovo. Traditional blue silk ceremonial scarf called khadag is tied to it. This scarf symbolizes mountain spirit Tengger (Tengri). What follows is lighting a fire and making food offerings. Ritual continues with a ceremonial dance and prayers. Everything ends with a feast.