The 25km hiking trail from Skógar, over the Fimmvörðuháls pass between the Eyjafjallajökull and Mýrdalsjökull ice caps, then down the other side to Þórsmörk, offers spectacular views and traverses lava from the 2010 eruption at Eyjafjallajökull. Although it’s feasible to do the whole thing in under ten hours, many people spread the trip over two days, overnighting at one of the two mountain huts en route, for which bookings are essential. The trail is usually passable without equipment from around mid-June to September; outside these times you’ll probably need an ice axe to cut steps during the descent to Þórsmörk, and possibly crampons. Whatever the time of year, come prepared for possible rain and snow, poor visibility and cold; the track is easy to follow in clear weather, but play safe and carry a compass and Mál og menning’s Landmannalaugar-Þórsmörk-Fjallabak map.
The trail starts by taking the staircase up Skógarfoss, then follows the river uphill over a muddy, shaly heath carpeted by thick patches of moss. There are many small waterfalls along the way, each of them unique: some twist through contorted gorges, others drop in a single narrow sheet, bore tunnels through obstructive rocks, or rush smoothly over broad, rocky beds. Around 8km along you cross a bridge and leave most of the vegetation behind for a dark, rocky plain flanked by the smooth contours of Eyjafjallajökull and Mýrdalsjökull. It’s another hour from here, following marker poles across gravel and snowfields, to the recently refurbished Baldvinsskali hut (fi.is; 5000kr). Alternatively, push on for another forty minutes to the larger second hut, Fimmvörðuskáli (893 4910, utivist.is; 5500kr), actually just west off the main trail.
From here you’re halfway along and crossing Fimmvörðuháls (1043m), the flat pass in between the two glaciers; there’s a pale blue tarn and then a gentle ascent to where the path weaves around and over the rough lavafields created in 2010. You end up at the top of a slope with a fantastic vista of Þórsmörk laid out below, Mýrdalsjökull’s icy outrunners hemming in the view to the east. The slope is snow-covered well into the summer and the quickest way down is to cautiously slide it on your backside, using your feet as brakes. This brings you to Heljarkambur, a narrow, 50m traverse with a vertical rockface rising on one side and a steep snowfield dropping 75m on the other; winds here can be appalling. At the far end is the flat, muddy gravel plateau of Morinsheiði: look at where steaming new lava is dispersing the glacier edge in a noisy waterfall at the neck with Heljarkambur. Cross the plateau and it’s a straightforward descent to Þórsmörk (though the short, knife-edge “Cat’s Spine” ridge can be nervous work, despite a helpful chain) and the Básar hut.