You start before dawn or in the low afternoon light, pulled out of Reykjavik and onto a ribbon of asphalt that gives way to black rock and wind. The ATVs hum under you as the city drops behind and the world becomes basalt and steam. Ahead rise green-grey slopes of Hengill, steam leaking from fumaroles like a slow-breathing animal. The scent of sulfur is sharp; the ground beneath you is older than most nations. A few minutes off the track you dismount at a steaming pool—Volcanic Springs—where other riders lower their shoulders and let the heated water take the edge off.