The Ijen vulcan’s crater (located in east Java Island, Indonesia) have a Blue Flame phenomenon, that there are only 2 in the world (the other one is in Iceland), and can be seen only at night. This is liquid sulfur, which has caught fire and burns with an eerie blue flame. Acidic gases emerges from the fumaroles among yellowish chunks of sulfur, and burns liquid sulfur. There, inside the Kawah Ijen crater, a one-kilometer-wide acidic crater lake lies in the middle. Visit planedia.com to see more cool stuff around the world!