Eptapyrgio — "Seven Towers" in Greek — is the fortified citadel at the highest point of Ano Poli, perched at the top of the Byzantine city walls that wrap around the upper town. The structure is a Byzantine-Ottoman palimpsest: the original towers were built in the 14th century and then extended and modified during the long Ottoman occupation. Most of it is now open to explore without paying.
Climb to the top of the walls for the best view in Thessaloniki: the whole city spread below, the bay and the Thermaic Gulf beyond it, and on clear days the cone of Mount Olympus to the south. The walk up from the lower city takes about 30 minutes through the lanes of Ano Poli — take the outer path along the walls back down for a different perspective.