Harnanca rises some 400 metres above the Two Moor Hills and the fortress sits atop it, giving an impressive vantage to observe the comings and goings on the downs below.
The fortress is reached by a series of ramps and stairways which wind and switch back up the steep eastern face of the hill. There is a guard post at the bottom of the path where it crosses a ravine by a narrow stone bridge.  The post house consists of a walled compound on the far side of the bridge with 5 m high stone walls with battlements and a huge, thick oak door sheathed in iron and decorated with curvilinear hobgoblin motifs of skulls. Beneath the compound is a warren of caves where the hobgoblins hid from the sun during daylight hours.
There is a hidden way up the southern face of the Harnanca but anyone coming up this way in daylight is likely to attract the attentions of the Fire Drakes, especially at dawn or dusk.