Boudhanath Stupa. According to legend, Boudhanath Stupa was built by an an old poultry woman who asked the king for land to construct a shrine to the Buddha. The king agreed, and offered her as much land as she could cover with the skin of a water buffalo. The woman proceeded to cut a buffalo hide into thin strips, and placed them end to end to form a huge circumference. The king realized that he had been tricked by the old woman, but he adhered to his word, and the stupa was constructed according to these dimensions. Nowadays, the stupa is the most popular site for Buddhists in Nepal, and throughout the day pilgrims can be seen circumambulating the structure chanting mantras. It is especially spectacular at night when adorned with butter lamps. Remember to walk around the stupa in a clockwise direction and also to spin the prayer wheels clockwise. There is a small entry fee to enter the stupa area, though this is waived for guests of hotels located at the other side of the stupa.
Source: http://wikitravel.org/en/Boudhanath