Mount Rinjani is a 3,726-metre volcano on Lombok with a lake inside it. Its summit ridge curls around a caldera roughly 6 by 8.5 kilometres across. On the floor lies Segara Anak, the "Child of the Sea," a crescent of turquoise water more than 200 metres deep, with hot springs at one edge. Rising straight out of that lake is Barujari, a young cone that still smokes and stirs. Rinjani is the second-highest volcano in Indonesia, and to the Sasak people of Lombok it is sacred ground rather than a summit to collect. The caldera itself is a scar: the mountain that stood here blew apart in 1257, in one of the largest eruptions in recorded human history.
Climbing Rinjani takes days, not hours. From the eastern village of Sembalun the trail crosses open golden savanna before tilting up to the crater rim, where trekkers pitch their tents and watch the light drain off the caldera. That walk up runs seven to ten hours, and the Sembalun rim camp sits at 2,641 metres. Long before dawn you set out for the summit, over loose ash and rock that slides half a step back for every step up. Protected as a national park since 1997 and named a UNESCO Global Geopark in 2018, Rinjani is also a living hazard: the 2018 Lombok earthquakes shook landslides down its slopes and stranded hundreds of trekkers. The trek now closes through the January–March rains and every climber needs an e-Rinjani permit and a licensed guide, but the mountain remains very much awake.