Byzantine monument — Didymoteicho, ~90km north of the city
Didymoteicho sits at the meeting point of the Evros and Erythropotamos rivers, and its hilltop fortress is the reason the town existed at all: an ancient and medieval citadel complex whose surviving 24 towers make it one of the most intact Byzantine fortifications anywhere in Greece.
The fortress briefly hosted the Byzantine imperial court at points in its history, before falling to Ottoman forces as one of their first footholds in Europe. Walking the walls gives a genuine sense of scale that photos from the base below don't capture.
Pair it with the Bayezid Mosque and the old Ottoman bath in the same town for a half-day that covers the site's full Byzantine-to-Ottoman arc.