Located 2.5km north of Halki, just below Moni, the small, peaceful Panagia Drosiani is among the oldest and most revered churches in Greece. Inside is a series of cavelike chapels. In the darkest chapels, monks and nuns secretly taught Greek language and religion to local children during the Turkish occupation.
Several frescoes still grace the walls and date from the 7th century. Look for the depiction of Mary in the eastern chapter; the clarity and expression is incredible.