Hengill

From Route 1 on Hellisheiði, turn off towards the Hellisheiði power plant (Hellisheiðarvirkjun), drive past it and take the side road to its end in Sleggjubeinsdalur, where a large gravel car park has a map board of the Hengill trails. The path climbs steeply out of the valley (one section has metal steps) to the pass Sleggjubeinsskarð, about 1 km from the car park. Here the loop splits: the usual clockwise direction takes the left fork, marked with black-tipped stakes, up the western slopes. The path gains the ridge and follows it north-north-east, then climbs a steep, eroded, rocky slope and crosses a short, narrow passage between two rock pillars where the packed earth is slippery and a slip could be serious. A flat, barren plateau follows, where markers are widely spaced and navigation is hard in cloud. The final climb has a short eroded step where hands may help, and a fork: in summer the direct line goes up a rocky gully that holds snow late into the season; the marked winter/spring bypass (Hjáleið Sleggjubeinsdalur vetur/vor) goes further east over the Hengill top. The summit, Vörðu-Skeggi, carries a cairn and is reached after about 7 km. Descend south to a junction and follow the path down towards Innstidalur, steep in its lower part, past a large steaming geothermal area and a private cabin, wade or hop the streams and join the blue-marked Hveragerði trail back west across the grassy, sometimes boggy valley to Sleggjubeinsskarð and the car park. ON gives 13.3 km, 705 m of ascent and 5–6 hours for the loop; the tuffmoss hiking guide gives 14.5 km and 740 m. In winter and early spring crampons and an ice axe are needed, and the lingering snow in the ravine at the top of the western slope makes that part dangerous. The Innstidalur path can be wet well into spring; ON asks walkers to turn back rather than damage it.