There’s so much to do in Thessaloniki, you’ll find yourself spoiled with the options. In the north of the city you’ll find the ancient city walls from the Byzantine era and the 16th century fortified White Tower, which serves as the city’s symbol. The Upper Town features the greatest landscape of traditional old houses and quaint cobbled streets, as well as the the Byzantine citadel, the Heptapyrgion Fort. The Byzantine Churches of Agios Demetrios, Agia Sofia and St. Nicolaos Orfanos are a must-see when visiting the city, as all three are on the list as UNESCO World Heritage Sites. Of all of the churches in Thessaloniki, the oldest is the Rotunda. The Rotunda began life as a temple to Zeus and is almost as old as the Pantheon in Rome. Owing to its rich and diverse history, the city also boasts a great many museums and galleries exhibiting works from many different eras.