Take the winding path from the road up the hillside to view the remnants of the ancient Commagene capital of Arsameia, passing stelae, stone reliefs and caves on your way to the hilltop. On the summit sits the jumbled toppled masonry of Mithridates I's palace and you'll be rewarded for your sweat by panoramic vistas of the surrounding countryside.
The first monument on your way up the trail (on the left after about 100m) is a large stele depicting Mithras (or Apollo), the sun god. Further along are the bases of two stelae depicting Mithridates I and Antiochus I, the latter (on the taller stele) holding a sceptre. Behind them you can peer into a deep underground food-storage chamber.
Further uphill is a superb stone relief portraying Mithridates I shaking hands with the ancient hero Heracles. Adjacent, a tunnel descends 158m through the rock to a chamber that was used for religious rites; a lot of loose small stones make the tunnel's steps difficult to negotiate and it's blocked by boulders about halfway down. The long Greek inscription above the tunnel entrance describes the founding of Arsameia; the water trough beside it may have been used for religious ablutions.
From the Kocahisar turn-off, another 1.5km south along the road brings you to the signposted Arsameia turn-off heading east. Arsameia is about 1.5km down this road.
