Church of Agia Ekaterini Syntagma & Plaka

One of the few very old Byzantine churches that is open regularly, this is definitely worth a peek inside to see how an 11th-century space is still in vibrant use and adorned with bright frescoes. For a time it was the property of the Monastery of St Catherine in the Sinai Peninsula, which is how it took on that saint's name. In the front yard are some Roman ruins.