The Byzantine Walls are one of the best ways to understand Thessaloniki's shape. The surviving fortifications climb above Ano Poli, linking the lower city to the heights and giving long views over roofs, the Thermaic Gulf and the dense modern grid below.
They are not a single-ticket attraction so much as a walking spine through the upper town. Go late in the day if you can: the stone warms, the city softens, and Thessaloniki's layered Roman, Byzantine and Ottoman past becomes easier to read.