You can make an easy, satisfying 10km circuit of Þingvellir and the rift valley along marked trails in under three hours. Starting at the National Park Information Centre, walk a short way east along the road past the campsite until you see a marker for the 2km footpath to Hrauntún through a landscape of mossy rocks, lava pavements and dwarf birch scrub. Hrauntún is the site of an abandoned farm, still ringed by a lava-block wall. There isn’t a single tree on the site – clearing them all must have taken some effort.
Turn south and follow a well-used 3km track to Skógarkot, a sheep farm abandoned in the 1930s, whose ruined but strongly constructed stone buildings occupy a grassy hillock roughly halfway across the valley. It’s not a high position, but still elevated enough for you to take in a panorama of distant peaks and rift walls, and feel dwarfed by the scale of the Þingvallahraun lava flow which stretches all the way from the lake to Skalbreiður. From here bear west towards the church at Þingvellir – a further 2km along a decent trail – and then follow Almannagjá for a final 3km back to your starting point.