Kostas' apartment is a small, cozy, well decorated place on the hillside overlooking Thessaloniki. It has all the amenities the average traveller needs, and a beautiful view of the city. If you plan on walking, it's going to be a bit of pain - luckily, public transportation passes nearby. The only issue I had was the bathroom ceiling - I'm tall (a bit over 2m), and I couldn't stand up straight inside. It made showering a nuisance.
Kostas was quick to answer my questions and offer information, and he even left refreshments and tourist maps of the city waiting for us.