Gjirokastër can be divided into roughly two halves, the old town up on the hill, and the new town in the valley below. You can walk just about anywhere if you're able to handle the steep cobbled streets. Taxis are cheap and there is a public bus circuit that connects the old town and the new town for about 30 leke. From the roundabout at the center of town to the bus station on the National Road is a fairly flat, easy, 10 minute walk along the main boulevard. Taxis will make this trip for around 200 leke.
