Kathmandu’s 36m-high Boudhanath Stupa is the largest stupa in Nepal, and one of the largest in the world. It is a religious centre for Nepal's considerable population of Tibetans. It supposedly dates from 5C AD. With three square tiers surrounding the central circle of the dome, Boudhanath is built in the form of a mandala, a symbol of the universe that is often used in Buddhist meditations.