32 Once-in-a-Lifetime Experiences to Add to Your Bucket List

15. Witness the "Blue Fire" of the Ijen Volcano, Indonesia

Most volcanoes spew red-hot lava—but Mount Ijen in Indonesia defies the ordinary. In the dead of night, its crater glows an eerie electric blue, a rare and surreal phenomenon caused by the combustion of sulfuric gases escaping from deep within the Earth. To witness this otherworldly natural wonder, you’ll need to start your trek around midnight, hiking through the darkness to the rim of the volcano. From there, a steep descent leads into the crater itself, where ghostly blue flames dance across the rocky landscape, illuminating the sulfur miners who brave these extreme conditions daily. As dawn approaches, the world’s largest acidic crater lake reveals itself—a stunning turquoise expanse of water, surrounded by volcanic cliffs. The contrast between the midnight blue flames and the morning’s emerald-green lake is a sight you’ll never forget. Best Time to Go: April to October (dry season), when the skies are clearest for night hikes.