Indonesia's landscapes include mountains, coastlines and terraced rice fields, and Mount Rinjani on the island of Lombok, West Nusa Tenggara, is one of its better-known volcanoes. At about 3,726 metres above sea level, Rinjani is often cited as the second-highest volcano in Indonesia, after Kerinci in Sumatra, and lies within Gunung Rinjani National Park. It attracts both Indonesian and international trekkers, many of whom come for the views from the crater rim and the crater lake below.
Rinjani is a demanding multi-day trek rather than a casual walk, and difficulty depends a great deal on the route, the weather and your fitness. Several official routes are used, including Sembalun, Senaru, Timbanuh and Torean. The Sembalun route in East Lombok is a common choice for reaching the summit, while Senaru in North Lombok is often used for reaching the crater rim from the forested northern side. Many trekkers go up one route and come down another.
The Sembalun route begins with long sections of open savanna. There is little shade here, so sun protection, a hat and plenty of water are important, especially in the middle of the day; later in the afternoon the temperature is usually more comfortable. The trail passes a series of numbered rest points, known locally as "Pos", before climbing steeply to the camp at Plawangan Sembalun on the crater rim. Water sources along the way are limited and not always reliable, so carry enough drinking water and ask your guide where it can be refilled.
Conditions on the mountain change through the day. Mornings on the crater rim can offer wide views over the caldera, and on clear nights away from city lights the sky can be full of stars. Nights at altitude are cold, often close to freezing near the summit, so warm layers, a good sleeping bag and a windproof jacket are essential. The final push to the summit usually starts in the early hours of the morning on loose volcanic gravel and is considerably harder than the lower sections.
Inside the caldera lies Segara Anak, a crater lake that many trekkers include in their itinerary. It can be reached from the crater rim on both the Sembalun and Senaru sides, but the descent and climb back out are steep and add significant time, so it is usually visited on a trek of three days or more. Around the lake, visitors commonly camp, and there are natural hot springs nearby where people bathe; local residents also fish in the lake. The area is considered sacred by many Sasak and Balinese Hindu communities, so behave respectfully and take all rubbish back down with you.
Climbing Rinjani requires registration with the national park, and trekking is normally done with a licensed guide and porters; rules, permit fees and opening periods change, and the trails are usually closed for part of the rainy season, so check current information from the park authority before you plan. Rinjani is an active volcano, and access can also be restricted because of volcanic activity or weather. Most visitors fly into Lombok International Airport or arrive by boat, then travel by road to the trailhead. Sembalun can be reached from Mataram in a few hours by car, typically via Aikmel in East Lombok, while Senaru is on the northern side of the mountain. Many visitors arrange transport through a licensed local trekking operator.