Though not one of Semnan's classic caravanserai villages, Padeh's sizeable shattered citadel, dating back at least 1500 years, has been so eroded by water and weather that it seems to be an almost abstract sculpture of hill-sized proportions. You can poke around in a preserved hammam site and pudding-shaped ice house amid many ruined old structures.
It's 5km off the Damghan–Garmsar Hwy, via the Aradan turning 93km west of Semnan, which is marked by a conical abambar (water cistern).