A former Byzantine fortress repurposed as a prison by the Ottomans and only decommissioned in 1989, the Eptapyrgion (‘Seven Towers’) is a grim reminder of Thessaloniki’s penal past, recounted in the Greek blues songs known as rembetika. Reached by a steep walk to the heights of Ano Poli, it's perfectly preserved, allowing access to some towers (of which there are actually 10), communal blocks and isolation cells, and displaying historical information and scattered artworks.
The views from the Byzantine walls are the best in the city.