You paddle around the vast turquoise waters enshrouded in vapor, your face bedaubed with the restorative silica mud that’s ladled out of pots along the perimeter. Set in a desolate Icelandic lava field between downtown Reykjavík and the airport, the Blue Lagoon is a primal lost world—one that owes its existence to a geothermal power plant. In 1976 engineers drilled 6,000 feet into the volcanic rock and brought up superheated, mineral-rich water, which after being harvested for electricity and discharged into a pool (at around 100 degrees) was discovered to have potent therapeutic qualities. Thus Iceland’s famous accidental spa was born. The facilities (offering steam baths, massages, and skin treatments) are currently undergoing an upgrade, due for completion this spring. The lagoon itself, however, remains blissfully untouched.