Laugavegur + Fimmvörðuháls (to Skógar)

The trail leaves Landmannalaugar straight into the Laugahraun lava field, where the tread threads between blocks of black lava under bright green moss, then climbs onto the plateau steadily rather than steeply over the first five kilometres. The surface turns to pumice, ash and loose obsidian, glassy black chips that skate underfoot on the steeper pitches, with fumaroles steaming beside the path and a hot spring at Stórihver. From there to about km 16 the walking stays high and open across a rolling waste of old snow, dark obsidian and stained rhyolite, dipping through a run of ravines where meltwater streams have cut in beneath the snow. This is the coldest and least sheltered ground on the route, and those ravine crossings are why it is slower than the distance suggests: the snow rots from below, so a crust thins without showing it. The stretch finishes with the long stony clatter down off Jökultungur, steep enough to want careful feet, with Tindfjallajökull, Eyjafjallajökull and Mýrdalsjökull all in view on a clear day, onto green moss and flat ground at the bottom.

Logistics: The hut at Hrafntinnusker (km 10.2) is the only building between the two ends of this stretch, and FÍ describe its supply track as almost impassable and used only occasionally, so nothing can be brought to you here and nothing can take you out.

Navigation: Posted the whole way and busy in season, so in clear weather a line of walkers is usually the clearest marker there is. The problem here is visibility rather than route choice: on the snowfields either side of Hrafntinnusker there is nothing to steer by except the posts, and cloud settles on this plateau and stays. Two memorials stand beside the path, one to a walker who died in a blizzard in late June within sight of the hut, which is a fair indication of what going wrong on this ground looks like.

Four quite different pieces of walking strung together, which is why one ascent figure flatters it. From the Grashagakvísl flats to Hvanngil the ground is green and comparatively sheltered, ash and cinder vehicle tracks past a big lake, with the first easy fords in it. Then the route commits to the black sand for a dozen kilometres, flat and dark and scattered with lava bombs, quick underfoot with nothing at all to hide behind. After Emstrur it turns to canyon country, moss over rock, with a steep drop and a steep climb either side of the footbridge in the Fremri-Emstruá gorge and a last cold wade across the wide gravel bed of the Þröngá. Þórsmörk then arrives all at once: birch woods, shelter, shade and roots underfoot, the first real green since Landmannalaugar. It does not last. The section ends by climbing straight back out from Básar, roughly 760 m in six and a half kilometres, up the Strákagil gully and along the narrow ridges of Kattarhryggir and Heljarkambur onto the edge of the pass.

Logistics: Walkers continuing over Fimmvörðuháls have to cross the Krossá between Langidalur and Básar on a movable footbridge. It is placed where the wardens judge the channel safe, it shifts during the season and it is taken out in severe flood, so do not fix a crossing point from an old GPX track.

Navigation: Well marked and mostly obvious, but three things catch people. Ford crossing points are marked and shift slightly year to year as the braided channels move, so cross where the markers put you rather than where the water looks shallowest. Emstrur is invisible until the last moment, which unsettles walkers counting it down. And on Morinsheiði the tread is faint across cinders with sheer drops on several sides, which is the one place above Þórsmörk where losing the line in cloud is dangerous rather than merely annoying.

The top of the pass, then sixteen kilometres of almost unbroken descent. The first three kilometres are what people come for: the 2010 lava of Goðahraun between the craters Móði and Magni, jagged and still unconsolidated, with Eyjafjallajökull on one side and Mýrdalsjökull on the other and snowfields lying between them well into the summer. It is high, flat, featureless and marked by yellow poles, and in cloud it is exactly as blank as that sounds. Past Baldvinsskáli the ground and the interest fall away together: a long stony 4x4 track down cinder fields, easy going and dull. The route comes back to life at the footbridge over the Skógá, where the track ends and a path takes over along the lip of the river gorge, staying with it for the last eight kilometres past a chain of some 26 waterfalls to Skógafoss and the staircase down to the road. That lower path is earth and grass rather than rock, so it is also the one part of the route that gets properly muddy.

Logistics: There is very little surface water on the pass because the lava and cinder drain it away. The mapped tap at Baldvinsskáli is recorded as available only at certain times or when the hut is guarded, and the Skógá at km 69.8 is the first crossing that can be counted on, so fill up in Þórsmörk rather than on the climb.

Navigation: Yellow poles carry the line across the lava and snow of the pass and are the only guide there is up there. Two things confuse people. There are two huts, Fimmvörðuskáli about 500 m west of the line and Baldvinsskáli on it, and walkers have reported two sets of same-coloured markers in that area which diverge and then rejoin. Below the Skógá bridge navigation stops being a question at all: the river is beside you the whole way down.