Ijen volcano (2 h hike), the extraterrestrial blue volcano with the world's largest and deadliest acidic lake, is located in a beautiful less populated Ijen National Park in East Java. Quiet swift roads, tranquil nights and pristine nature accompany this experience.
The great crater is filled with concentrated sulfuric acid, and a sulfur mine is producing a toxic cloud of gas, making it clear that this place is a private realm of the planet itself tolerating no permanent wildlife.
The foothills area of Ijen, however, is populated with rare species of monkeys and birds, and features some endemic species of butterflies and flora.