The imposing hisar (citadel) is the most interesting part of Ankara to poke about in. This well-preserved quarter of thick walls and intriguing winding streets took its present shape in the 9th century AD, when the Byzantine emperor Michael II constructed the outer ramparts. The inner walls date from the 7th century.
After you've entered Parmak Kapısı, the main gate, and passed through a gate to your left, you'll see Alaettin Camii on the left. The citadel mosque dates from the 12th century, but has been extensively rebuilt. To your right a steep road leads to a flight of stairs that leads to the Şark Kulesi, with panoramic city views. If you look to the north from here you'll see the Ak Kale (White Fort). It is out of bounds to visitors, though there are more good views from near its hilltop perch if you follow the alleyway leading up to the tower.
Some local families still live inside the citadel walls and the houses here often incorporate broken column drums, bits of marble statuary and inscribed lintels into their walls. For a long time the neighbourhood here was extremely run-down but the past few years have seen the area gentrified somewhat, although once you duck off the main route there are still many narrow, ramshackle alleys to explore.