Although 6km east of town, this fascinating museum of science and technology, old and new, is worth visiting. There's a planetarium, a giant-screen cinema and simulator for the kids, while the exhibition of ancient Greek technology shows just how ingenious the ancients really were. Opening times and pricing can be unnecessarily complicated: check the website, and expect sometimes to have to buy separate tickets for the sections you wish to see.
Noesis
Thessaloniki