The Mariamite Cathedral of Damascus (also called the Virgin Mary Greek Orthodox Cathedral) is the seat of the Greek Orthodox Patriarch of Antioch and All the East. The original church on this site was founded in the 2nd century; the current building dates mostly from the late 19th century, with parts of the older fabric preserved inside.
The interior is full of dark wood, gilded icons and silver lamps. Sunday liturgy is sung in Arabic in the Byzantine rite — worth attending if you happen to be in town, even as a non-Orthodox visitor. The cathedral is in the heart of the Bab Touma quarter and easy to combine with other Christian sites.