Drepung is the largest monastery in Tibet. It is, along with Sera and Ganden, one of the "great three" monasteries of the Gelukpa school. Drepung was founded in 1416 by Jamyang Chojey a disciple of Je Tsongkhapa the founder of Gelukpa. Prior to the Chinese invasion of Tibet in 1959 the monastery housed around 15000 monks, at present just a few hundred due to a government policy capping monastery populations.
Prior to the Chinese invasion Sera housed 5,000 monks, now, like Drepung the population is a few hundred. Sera was founded in 1419, by Jamchen Chojey, a disciple of Tsongkhapa. Sera means 'Enclosure of Roses'. Both Sera and Drepung are close to Lhasa and can be reached by public bus. Buses pick up passengers along the main street of Lhasa.
Ganden is the original Gelukpa university monastery and was founded by Tsong Kapa himself in 1409. Ganden sits on Wangbur Mountain at an altitude of 4,300m. The Ganden Monastery was completely destroyed following the Chinese invasion of Tibet in 1959, and since the 1980s has been re-building.