As other reviewers we found the flyer in our Plovdiv Hotel and simply went to the front door of the Post Office on the central square. Vessy, our guide, was a little surprised about the number of waiting people, but she managed to keep the group together and stick to the stated 2 hours. We walked along the shopping street and at the stadium we turned to the old town. We saw most of the interesting wooden houses there and could also catch a glimpse into the yard of the Sveti Konstantin i Elena Church although it was a high church holiday. We finished the walk on top of Nebet Tepe right in time for the beautiful sunset over the city. And yes, the tour is really free – surely a donation is highly welcomed and well earned!