I have very nice memories to the trip to northern Greece in June 2006. I managed to visit two promising TWHS (Zagorochoria and Mount Olympus) and two excellent WHS: paleochristian monuments in Thessaloniki and the rock city with monasteries in Meteora.
To visit the Meteora site, we traveled by bus from Ioannina via Metsovo to Kalambaka/Kastraki. Then, we did a loop by walking along the asphalt road that goes through the rock city. We did stopovers to visit the Roussanou monastery (PHOTO), where we joint the guided tour, and also the Holy Trinity monastery, which we visited for free but without stepping inside. We spent a night in a tent on dry meadow full of ants in the eastern part of the rock city complex (I am not sure if it is legal now but such were the times...) Unsurprisingly, this WHS was very touristy and overcrowded by visitors. The advantage of our walking and staying at the site regime was that we were a bit incoherent with the constant flow of tourist groups in buses and cars. The weather was hot but still bearable, fortunately we "survived" the heavy rain storm inside the Roussanou monastery.
To sum up: the site is really a world class, and I was happy for the opportunity to explore the site for two days.