The Ijen Plateau in East Java holds one of nature's most extraordinary spectacles: the blue fire of Kawah Ijen, where burning sulfuric gases ignite into vivid cobalt flames that flicker across the crater floor in the hours before sunrise. The trek begins at midnight, ascending through pine forest to the crater rim before descending to the lake's edge — a caldera filled with the world's largest acidic lake, shimmering in shades of teal and aquamarine. A guide, headlamp, and gas mask are included. Sunrise over the crater rewards the effort with views that stretch across the volcanic landscape of East Java and Bali.