Fimmvörðuháls – Skógar to Fimmvörðuskáli
The 25-kilometer Fimmvörðuháls, or Five-Cairn Trail, leads from the Skógafoss waterfall, up and between two glaciers, and into the valley of Þórsmörk. One of Iceland's most popular hikes, it's often done over two days, with a night in the Fimmvörðuskáli hut, but we pushed ourselves to complete the whole thing at once. Ten amazing hours.