Kawah Ijen is a mysterious crater lake, located at the core of a reserve that spans the slopes and summits of three volcanoes. It is one of the most acidic lakes in the world and the site of a labor-intensive sulfur mining operation. Every day an elite class of hardened men known as the ‘sulfur slaves’ tirelessly hump baskets of yellow rocks, weighing up to 200 pounds, from the lake’s edge, up to the crater rim, and then back down the side of the mountain.

   The lake is milky turquoise in color, and its mineral purity and surrounding volcano walls provide a surreal sight, especially at night, when the combustion of sulfuric gasses emerges in the form of blue fire.