Not widely known archaeological site, but particularly dear to the Thessalonians, the Roman Agora with its subterranean museum and its amphitheater is one of the places worth visiting if you stop in Thessaloniki for a few days.
The site is located above Dikastirion square, which in turn is above Aristotelous square. The entrance costs 3€ and includes the museum. The site is open every day except Monday from 8 to 15,it is possible that the opening time is extended during summer. Beware that the museum is only open from Tuesday to Friday.