I joined a guided hike to Hrafnabj÷rg, near Ůingvellir, with Utivist (the Icelandic Touring Association). It was quite a desolate place, and a freezing cold day, yet the sun was shining brightly and it was nice to chat with the locals.
Most of the hike was over lava fields. The lava fields make for a terribly uneven and treacherous surface. But, when covered with lichen, the rocks do provide a wonderfully cushioned footfall (so long as you don't roll your ankle).