If you're looking for a unique adventure, visiting the monasteries that are part of the Meteora area of Greece may be something to put at the top of your list when travel resumes in earnest!
Located near Thessaly, Greece, there are several different monasteries that are possible to visit based on different access and tour options. The Monastery of St. Stephen seems to be the easiest one to start, though I wouldn't necessarily rule out the others if you have a few days open. Housing several cathedrals and a chapel, the primary cathedral at this monastery dates back to the 16th century.
Access to Greece may be the best via train or bus with numerous options from Athens International Airport to Kalabaka direct.