Gunnuhver

Gunnuhver is Iceland's largest mud pool, a furiously steaming vent on the Reykjanes Peninsula where seawater seeping into the hot ground is flashed to vapour and spat back out as boiling grey mud. Set in a raw field of cracked, sulphur-stained earth near the peninsula's tip, it is one of the most violent-looking geothermal spots in the country.

Its heat comes from the mid-Atlantic rift. Reykjanes sits astride the boundary between the North American and Eurasian plates, and magma close to the surface superheats groundwater to well over 100°C. The main vent has repeatedly destroyed the viewing platforms built around it, a reminder that this is scenery to watch, not touch. There is no bathing here.

Folklore gives the place its name. Legend tells of an angry ghost, Gunna, lured into the spring and trapped there forever; the story suits the roaring column of steam and the smell of sulphur that hangs over the site. Wooden walkways keep visitors at a safe distance from the scalding ground.

It anchors a wider volcanic tour. Nearby stand the Reykjanes lighthouse, the Bridge Between Continents spanning the rift, and, in recent years, fresh lava fields from eruptions near Fagradalsfjall. The peninsula is the first thing many travelers see, as Keflavík Airport is minutes away. Any season works on the paved approach road, though winds off the Atlantic can be fierce; summer gives the calmest light, while low winter sun makes the steam glow. Gunnuhver is a short, powerful stop beside boiling earth where two continents pull apart.