Boudhanath at sunset

Boudhanath (Devnagari: बौद्धनाथ) (also called Boudha, Bouddhanath, Bodhnath or Baudhanath or the Khāsa Caitya) is one of the holiest Buddhist sites in Kathmandu (Yambu), Nepal. It is known as Khāsti in Nepal Bhasa Jyarung Khasyor in Tamang language, as Bauddha or Bodh-nāth by modern speakers of Nepali. Located about 11 km (6.8 mi) from the center and northeastern outskirts of Kathmandu, the stupa's massive mandala makes it one of the largest spherical stupas in Nepal.

The Buddhist stupa of Boudhanath dominates the skyline. The ancient Stupa is one of the largest in the world. The influx of large populations of refugees from Tibet has seen the construction of over 50 Tibetan Gompas (Monasteries) around Boudhanath. As of 1979, Boudhanath is a UNESCO World Heritage Site. Along with Swayambhunath, it is one of the most popular tourist sites in the Kathmandu area.

The Stupa is on the ancient trade route from Tibet which enters the Kathmandu Valley by the village of Sankhu in the northeast corner, passes by Boudnath Stupa to the ancient and smaller stupa of Cā-bahī (often called 'Little Boudnath'). It then turns directly south, heading over the Bagmati river to Patan - thus bypassing the main city of Kathmandu (which was a later foundation). Tibetan merchants have rested and offered prayers here for many centuries. When refugees entered Nepal from Tibet in the 1950s, many decided to live around Bouddhanath. The Stupa is said to entomb the remains of Kassapa Buddha.

Buddhist religious architecture developed in South Asia in the 3rd century BCE.

Three types of structures are associated with the religious architecture of early Buddhism: monasteries (viharas), stupas, and temples (Chaitya grihas).

Viharas initially were only temporary shelters used by wandering monks during the rainy season, but later were developed to accommodate the growing and increasingly formalised Buddhist monasticism. An existing example is at Nalanda (Bihar). A distinctive type of fortress architecture found in the former and present Buddhist kingdoms of the Himalayas are dzongs.

The initial function of a stupa was the veneration and safe-guarding of the relics of the Buddha. The earliest surviving example of a stupa is in Sanchi (Madhya Pradesh).

In accordance with changes in religious practice, stupas were gradually incorporated into chaitya-grihas (temple halls). These reached their high point in the 1st century BC, exemplified by the cave complexes of Ajanta and Ellora (Maharashtra). The Mahabodhi Temple at Bodh Gaya in Bihar is another well known example.