About 1.5km south of the Kocahisar turn-off, a turn to the east brings you to a national park gate and ticket office and, 1.5km past this, the ancient Commagene capital of Arsameia. Here a path leads 400m uphill from the road, past several intriguing monuments, to the jumbled-stone ruins of Mithridates I's palace on a hilltop with superb panoramas.
First up on the left after about 100m is a large stele depicting Mithras (or Apollo), the sun god. Further along are the bases of two steles 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.