This small but significant 12th-century marble church consecrated to two saints is worth paying a visit. Standing next to the Metropolitan Cathedral of Athens, it is also known as the Little Metropolitan Church. Peek inside and admire the plaques and sculptures.
Wikipedia https://en.wikipedia.org/wiki/Little_Metropolis
Athens Info Guide website http://www.athensinfoguide.com/wtschurches/panagiagorgoupekous.htm
Address Plateia Mitropoleos 6-9, Athens 10556, Greece
Coordinates 37°58'30.052" N 23°43'47.986" E