Out of the blue: From a distance, the turquoise water of the crater lake at Indonesia's Kawah Ijen volcano looks picturesque. But it's a steamy, sulfur-filled hell down there. The 200-meter (656-foot) deep lake is one of the most acidic in the world, so acidic it can dissolve fingers and clothing. Miners tread down into the crater to collect blocks of bright-yellow sulfur, which forms when gaseous and molten sulfur emerges from fumaroles -- volcanic vents -- and hardens. Above, a miner carries sulfur out of the crater on July 22, 2006.