Drepung Monastery, located at the foot of Mount Gephel near Lhasa, is the largest of all Tibetan monasteries and one of the "great three" Gelukpa university monasteries of Tibet. Today the population at the monastery located in Tibet is much smaller with merely a few hundred monks, due to population capping enforced by the Chinese government.

Sources, related links:
Wikipedia - Drepung Monastery
Tibetan & Himalayan Digital Library - The Drepung Monastery Project