Kawa Ijen volcano in Java, Indonesia

This is the Kawa Ijen volcano (or Ijen volcano as Kawa already means crater). The crater is huge and houses an acid lake (you can still dip your finger inside though, it won't dissolve) and a sulfur mine. Miners carry 70kg of sulfur on their backs back up to the ridge and then down the volcano, wearing sandals and no gas mask. Respect!