Mount Bromo and Mount Rinjani
The Indonesian archipelago is thought to boast more active volcanoes than anywhere else on Earth. Mount Bromo, standing 2,329 feet tall, is the most-hiked mountain in Indonesia and sits inside the massive Tengger crater, surrounded by the six-mile-long Laut Pasir (sea of sand). Horseback-riding is popular, where you navigate the Laut Pasir to the bottom of the steep stairs that lead to the crater. The crater's usually busiest for tourists around 5:30 a.m. — right around sunrise.
Experience it: Exodus Travels has an 11-night Indonesia Volcano Trek itinerary that includes Mount Bromo.