A great place to start a tour of Thessaloniki is with an iconic symbol of the city, the Lefkos Pyrgos (Λευκός Πύργος), or White Tower, an important Ottoman monument. It was built around 1535, possibly by Ottoman master architect Mimar Sinan, to replace an older Byzantine tower and is the last surviving tower from the Ottoman walls.
During Ottoman occupation, the Lefkos Pyrgos served as a prison, fort and garrison and was also called the Red Tower or Blood Tower from the tortures and mass executions that occurred there. It was whitewashed in 1912 when Thessaloniki was liberated and reunited with the rest of Greece.
Visitors are able to climb up to the top. Each level on the way up has a small exhibit about the history of Thessaloniki. Once at the top, the views are breathtaking. Admission (as of July 2016) between April and October is €4. The rest of the year it’s €2. The official website has more info.
One of my favorite views of the tower is while walking along the sea down Leoforos Nikis.