Mount Rinjani: Lombok's volcano, and the trek to its rim

Mount Rinjani dominates Lombok the way Agung dominates Bali, except that Rinjani is higher, harder and has a lake inside its caldera. The summit is 3,726 metres, the second-highest volcano in Indonesia, and the trek to the rim has become one of the country's signature hikes.

It is not a walk. The standard two-day trek climbs 1,500 metres in a day, camps on a exposed ridge at 2,600 metres, and descends the next morning on loose volcanic scree. The three- and four-day versions add the lake, the hot springs and the summit. None of them is easy, and all of them reward the effort.

The routes: Sembalun and Senaru

There are two main approaches. Sembalun, on the eastern side, is the shorter and steeper route to the crater rim, a climb through savanna and pine forest that takes five to six hours to the camp at 2,639 metres. Senaru, on the northern side, climbs through rainforest to the rim above the lake and is the route most people descend.

The classic itinerary is a two-day trek up from Sembalun and down to Senaru, camping on the rim in between. The three-day version adds a descent to the lake and the hot springs. The four-day version adds the summit — a 2 a.m. start, two hours of scree and a narrow ridge — and is only for people who are fit and acclimatised.

What the trek actually involves

The first day is a steady climb of about 1,500 metres, much of it on an exposed ridge with no shade, followed by a short scramble to the camp. The camp is on a saddle at 2,600 metres, with a view over the lake and the cone of Gunung Baru, and the temperature at night drops to near freezing.

The second day descends to the lake (about two hours), crosses to the hot springs, and climbs back up to the rim before the long descent to Senaru. It is eight to ten hours of walking, much of it on loose rock, and the knees take a beating. The summit add-on is a 2 a.m. start on scree, and the reward is a sunrise over the whole island.

Guides, porters and permits

You cannot trek Rinjani independently. The national park requires a registered guide, and the route is not marked well enough to follow safely in the dark. Porters carry the tents, food and water, and most operators employ local Sasak crews from Senaru and Sembalun.

A two-day trek costs about Rp 2,000,000 to 3,000,000 per person, and a three-day trek Rp 3,000,000 to 4,500,000, including permits, gear and meals. The price difference usually reflects the food, the quality of the tents and whether the porters are paid fairly. Ask about porter loads and wages before you book.

Fitness, altitude and the weather

The trek is strenuous but not technical. If you can walk uphill for six hours with a daypack, you can do the two-day rim trek; the summit day is harder because of the scree and the altitude. The camp is below 3,000 metres, so altitude sickness is uncommon, but the cold and the wind are serious.

The season runs from April to November, with the best conditions from May to September. In the wet season the trail is slippery, the views disappear and some operators stop running. Even in the dry season it rains on the rim, and the temperature at night can drop to 5°C or lower.

Inside the caldera: Segara Anak and Gunung Baru

Segara Anak is the lake inside the caldera, about six kilometres across and 200 metres deep, milky green from the volcanic minerals. The hot springs on the western shore are a set of rock pools where the water comes out at around 40°C, and trekkers on the three-day route stop there to soak their legs before the climb back up to the rim.

The cone of Gunung Baru rises straight out of the lake, black and steaming, and it is the youngest part of the complex: the mountain is still active, and the park closes the summit when it stirs. The lake is sacred to the Sasak and Balinese communities around the mountain, and offerings are still made at its shore.

Where to stay before and after

Senaru is a village of guesthouses at the foot of the northern route, with waterfalls, coffee gardens and views of the mountain. Sembalun is a farming village on the eastern side, with a handful of homestays and a cooler climate. Both are cheap, Rp 300,000 to 700,000, and both are used by trekkers acclimatising the night before.

Most operators include a pick-up from Senggigi or the Gilis, but the drive to Senaru is two hours and to Sembalun two and a half. Stay a night at the trailhead if you can; the 5 a.m. start is much easier when you are already there.

Getting there and what to bring

Senaru is 2.5 hours from Mataram and 3 hours from the airport; Sembalun is 2.5 to 3 hours from Mataram. The roads are winding and the last section is steep. Most treks include transport from Senggigi, the Gilis or the airport.

Bring layers: a warm fleece, a waterproof shell, a hat, gloves, a headtorch and broken-in boots. The porters carry the heavy gear, but you carry your own water, snacks and rain gear. Trekking poles are worth the rental, especially on the descent.

• Two-day rim trek: up from Sembalun, camp, down to Senaru.
• Three days adds the lake and hot springs; four adds the summit.
• Book through an operator that pays porters properly and limits loads.
• Pack for 5°C at night and 30°C on the descent, even in the dry season.

Questions people actually ask

How hard is the Mount Rinjani trek?

The two-day rim trek is hard but achievable for anyone with decent fitness: six hours uphill on day one, eight to ten hours down on day two. The summit add-on is significantly harder because of the scree and the early start.

Do I need a guide for Rinjani?

Yes. The national park requires a registered guide, and the trail is unmarked in places. Porters carry the camp gear, and the package price usually includes permits and meals.

What is the best route up Rinjani?

Sembalun for the rim, Senaru for the descent, which is the classic two-day route. Senaru is also the start for the lake and the summit on longer treks.

When is the best time to climb Rinjani?

May to October, in the dry season. The trail is safer, the views are clearer and the operators run regular departures. The wet season is muddy, cloudy and sometimes closed.