The closest is Fortress of Vardari, 1 km south-west of the city centre; the most famous is White Tower of Thessaloniki — #187 of 9,079 worldwide — 2 km south-east. The oldest dated site in the circle is Walls of Thessaloniki, founded c. 325 BC.
The 100 km circle reaches into 2 countries — Greece (9), North Macedonia (1).