Thessaloniki isn't exactly a city you're likely to visit for fun. Most people who go there do so because it is a convenient stopping off point for visiting places in northern Greece and has the second major airport in Greece. As such it seems somewhat unfair to criticize it for being a grungy mess because it isn't supposed to be anything else. Basically Thessaloniki is Athens without the Parthenon.
Avebury may make me change my mind about Neolithic sites. It was a beautiful town. We came there for lunch and the pub gave us a limited choice of food in order to accommodate all of us. The pub has a well that supposedly contains the body of a murder victim. You'd be surprised how many wells seem to have those but this one was built right into the pub and served as a table.On the way in we passed a giant mound that is apparently the biggest Neolithic monument in Europe. It's just a big mound of earth but it is impressive to consider its scale.
