The Monastery of Panagia Archaggeliotissa sits above Xanthi on the slopes north of town, close enough to feel connected to the city but high enough for a different mood. The monastery is an Orthodox pilgrimage site, and its ecclesiastical museum preserves icons, church objects, manuscripts, and other material tied to the local metropolis.
The setting is half the reason to go. From the hill you get a better sense of Xanthi's position between the old town, the plain, and the Rhodope foothills. Dress respectfully, check opening details for the museum, and combine the visit with the nearby paths and viewpoints if you want more than a quick religious stop.