From Lonely Planet: "The Buddhist temple of Swayambhunath, situated on the top of a hill west of the city, is one of the most popular and instantly recognizable symbols of Nepal. The temple is colloquially known as the 'monkey temple' after the large tribe of handsome monkeys which guards the hill and amuses visitors and devotees with tricks, including sliding gracefully down the double banisters of the main stairway to the temple. The roving monkeys quickly snatch up any offerings of food made by devotees and will just as quickly grab anything you might be carrying.
Geologists believe that the Kathmandu valley was once a lake, and legends relate that the hill on which Swayambhunath stands was an island in that lake. It is said that Emperor Ashoka paid a visit to the site over 2000 years ago. An inscription indicates that King Manadeva ordered work done on the site in 460 CE and by the 13th century it was an important Buddhist centre. In 1346 Mughal invaders from Bengal broke open the stupa to search for gold. Under the Mallas, various improvements were made and the great stairway to the stupa was constructed by King Pratap Malla in the 17th century."