Sera monastery was founded in 1419 by a disciple of Tsongkhapa named Sakya Yeshe. Before a monastery was built in Sera, Tsongkhapa had established hermitages in the cliffs above. Over the years, the monastery grew to have close to 6000 monks. Sera and Drepung monasteries became the largest Geluk sect monasteries in Tibet. Today Sera has around 600 monks.
Sera monastery is famous for its "monk debates" which take place nearly everyday of the week. The monks gather each afternoon to debate buddhist teachings and philosophy (pictured below). Though many monasteries across Tibet have debates, Sera is the best and most popular place to witness it.
Sera monastery is only 5km from downtown Lhasa. It can be easily reached by bus or taxi. Sera is a common place for tourists to go so you are going to have to buy an entrance ticket (only the most touristy monasteries charge an entrance fee). It is best to go in the afternoon in order to see the monk debates.