Kawah Ijen Volcano: This volcano in Java is known for holding the biggest turquoise crater lake in the world, as well as the only occurrence of "Blue Fire" in the world. It takes 3-5 hours of trekking from Banyuwangi in Java. One can also take the ferry from Bali.
One can observe sulfur miners at work, take a stroll around the rim of the crater, and capture pictures of the blue flames, which can only be viewed in the dark. The path is considered to be of medium difficulty and requires safety measures such as gas masks while approaching the blue flame.
Excursions from Banyuwangi or Bali can include guides, transport, and gear. The driest period, from April to November, gives the best visibility, although the early morning sun provides the best light in the lake. Kawah Ijen Crater is a ‘must-see’ location for volcano lovers and photographers.