Zeyrek Mosque ( Church of Christ Pantokrator ) is located Zeyrek area in Fatih distinct of Istanbul. This Church ,is date from the Byzantine period, made of three chapel. It has the largest floor, church after Ayasofya for a surviving historical building in Istanbul.

Between 1118 and 1124 Byzantine Empress Eirene Komnena built a monastery on this site dedicated to Christ Pantokrator. The monastery consisted of a main church also dedicated to the Pantokrator, a library and a hospital. After the death of his wife, shortly after 1124, Emperor John II Komnenos built another church to the north of the first dedicated to the Theotokos Eleousa ("the merciful"). This church was open to the population and served by a lay clergy. Finally a south courtyard and an exonarthex were added to the complex , and the two shrines were connected with a chapel, which became the imperial mausoleum of the Komnenos and Palaiologos dynasties. Besides many Byzantine dignitaries, Emperor John II and his wife Eirene, Empress Bertha of Sulzbach (also known as Eirene, and wife of Manuel I Komnenos), and Emperor John V Palaiologos were buried here. Shortly after the Fall of Constantinople the building was converted into a mosque, and the monastery was converted for a while into a Madrasa(school). Historical Info Source From : http://en.wikipedia.org/wiki/Zeyrek_Mosque - 16.07.2011

Zeyrek Mosque, is located Zeyrek area of Fatih distinct. It is next to Unkapanı distinct. Because of center location, you can use lots of Public bus to go. After Unkapanı station you get off and 5 minute walk to reach.
Public Buses - Zeyrek Area