Tim P
Google
Incredible history. Built by the Romans, converted church by the Byzantines, then into a mosque by the Ottomans, before finally returning to a church again in the modern day. It contains some of the oldest mosaics in the world. Each tile the size of a pinhead, and each one set at a different angle so they appear to glitter as light passes over them. Unmissable.
If you are curious, the tower outside is actually a minaret built by the Ottomans, but retained even after its conversion back to a church.