We kept the trekking from Landmannalaugar to Þórsmörk for the end. The distance to Þórsmörk is about 60 kilometers. Only the first day goes roughly 900 meters up, afterward its mostly downwards. The lag to Skogar adds a bit more than 20 km and another 900 meters up. The trail is very well known and during the summer season rather crowded. There is a hut every 15 kilometers, but in summer they are mostly full and have to be reserved in advance. There is no food on the huts and as we had not reserved we carried heavy packs with food for five days and all the camping equipment.
The trail starts in the interior of Iceland which is normally only accessible by four-wheel cars with waterproofed engine. The roads themselves are not the problem but the fords. The bus to Landamannalaugar is a four-wheel vehicle and has an enormous light space below. But not only the road, also the trek itself crosses several rivers. After heavy rain or thaw fording can become difficult.
We did the trip during the last days of August. Apparently the season is already over by that time, all huts have been completely empty. There are no more snow bridges across the rivers and fording is therefore trickier. The cracks on the small glacier just below the Fimmvörðuháls are a bit scary so late in the season.