Beautiful small church with wonderfully preserved mosaics and frescos. It's a bit of a jaunt out to it but well worth the effort. Bring a guidebook or two or you can spring for the audio guide as there are so many details you can miss otherwise. It can get crowded at certain times of the day due to tours but it's easy enough to find a spot to stand in and wait until everyone else moves on. Transportation wise, I took Tram 1 to Tram 4 (change at Topkapi) and got off at Edirnekapi and it was an easy 4 minute walk. I ended up taking the bus back but as they didn't announce stops I was glad I took the tram there. One of the few Istanbul attractions I went to that I would repeat for sure!