Each part of the architecture in this place has a symbolic significance. Take, for example, the eyes on all four sides of the tower, which represent the wisdom, compassion and omnipresence of Buddha. The symbol for the nose is the Nepali character for "1", which signifies unity and the one way to reach enlightenment - through the teachings of Buddhism.
Everyone here is walking in a clockwise direction around the stupa. The Boudhanath Stupa is also known as "The Stupa that Answers All Prayers", and it's believed that circumambulation will lead to the fulfilment of wishes. I didn't do it because I'm not Buddhist, but I thought the ritual was an enchanting one.
As some of the pilgrims walk they spin prayer wheels. These wheels bear an inscription reading "Om Mani Padme Hum", the mantra of the bodhisattva embodying compassion.