Kariye - Caria ( St. Saviour In Chora) Muzeum is located at Edirnekapı section in Fatih district of Istanbul. The name 'Kariye' derives from 'Chora' which means outside the city wall or 'rural' in old Greek. The district was thus before the land walls were built. In Byzantine Period it was church, after conquest it converted to mosque and it became a securilarized museum in 1948. The interior of the building is covered the fine mosaics and frescoes.
Google Maps - Caria ( Kariye ) Museum

The church building dates back to the 12th century, but frescoes and mosaics are from the 14th century. Chora remained in use as a church for sometime after the turkish conquest, being converted into a mosque by Beyazıt II. Today it is preserved as a historical monument, owning to the valuable mosaics and frescos. The mosaics were cleaned and restored by the American Byzantine Institude. The frescoes are among the finest examples of Byzantine art to be found anywhere in the world. They depict stories from the Bible as well as the life of Virgin Mary and Jesus Christ.

You can get off Metrobus - Edirnekapı station or Public bus Edirnekapı station. After you can walk 10 minute to follow sights to Kariye Museum.
Public Bus - Edirnekapı