Gunung Rinjani 3752m - 3 day trek traversing an exploded active volcano

Gunung Rinjani is the 2nd highest Mountain in Indonesia - its 10 km wide Caldera is filled with a crater lake and features a 300 years young new active volcanic cone at its centre. In 2013 volcanologists finally unveiled one of the big misteries and confirmed it was the explosion of Gunung Samalas in 1257 AC, which caused the deleterious small Ice Age around the World, bringing famine and social unrest to the middle age world (PNAS). Scientist are on their way back there in 2014, to search for the antique capital, which might be giving raise to a new 'Pompei of the East'.

Appended some pictures or Kanawa Island as well in Komodo NP.
 

Organisation

We organised the trek as a private group of 3. There are a plenty of trekking agencies to choose from and Rinjani Treks are offered throughout Bali and Lombok an the Gilis. Top trekking companies offer one porter per client, will take the rubbish down, will cook, carry food, water and the tents, etc. A superlative service indeed. Provided you have your own gear, it is possible doing this trek self catered, by hiring just a guide w/o porters, but of course this is then a good bit harder. I have heard that Joe Adventure is planning to start a gear rental service soon. 

Day 0 (200Hm up; 200 Hm down, 3h)

we travelled from Gili Air via local boat (20'000 Rp) to Bangsal harbour on Lombok, where a driver picked us up and drove 1.5h to Senaru (600m), to John's HQ and guesthouse. After lunch we hiked to and bathed in the stunning waterfalls in the jungle close to Senaru (3h return). Dinner and sleep at Johns very confortable guesthouse.

Day 1 (1700Hm up, 6h)

Start after breakfast at 6.30am and drive to Sembalung (1h), the trailhead at ca. 900m elevation. Starting from Sembalung has the advantage that summit day is on day 2, whilst when starting from Senaru (inverse) the summit is reached on day 3 only and the ascent on day 1 is 2000 m vertical. After paying the park entrance (150000 Rp pp) we start at 9.30 am. The 1st part is a phantastic savannah. The trail becomes steeper as we approach the volcano flanks. At post 3 we have lunch, prepared by our cook, and watch the many monkeys around us. We continue and the trails becomes steep and steeper, until we reach the crater rime at 2600m, where our porters will set up camp for us. Relax, doing Yoga, and watching a phantastic sunset, talk to many trekkers from other groups. After the great dinner, at 8pm we are in our tents.

Day 2 (1750 Hm up, 1750 Hm down, 13h)

This is a long day. Wake up at 2am, fried banana breakfast and start at 2.30am. We follow the trail along the rim: hike up a steep section before it becomes flattisch again and the last hour very hard hiking on steep volcanic scree to reach the summit. We are fast and overtake almost everyone to reach the summit as the second group, joining a group of Chilenos after a 3.30h. The summit is in deep cloud and we realise we wont see the sunrise. Anyhow, many pictures taken and we are very happy to be there! Right after 6am we start our descent, and just below the summit I witness one of the best sunrises I have aver seen through the clouds. Now only we see the stunning scenery around and below us: high above the clouds, with the stunning crater lake, the volcanic moonscape is simply breathtaking. SamX and [NatX] have fun running down the scree and I will see them only at the camp. I instead enjoy every second of this mystical descent in the sun. Back at camp we have a real breakfast, chill out for an hour, pack up and continue down to the lake. The path is very steep in places, but has been improved a few years ago with concrete and reilings, so it is non-technical. This is followed by a traverse across alpine meadows, which starkly remind of alpine meadows w/o cows, but actually are home to Edelweiss. After 2h we get to the lake and continue to the hot springs, where we can have a swim in pleasant 36C water. After lunch we continue around the lake and climb back up the other side to the Senaru crater rim on the N side. The views inside the caldera are breathtaking and the path up the caldera very steep. we get to the rime 14h after the start and are quite tired. We spend the pm walking around camp and admiring the stunning views from the crater rim. We are once again well above the cloud. The sunset is amazing, with holy Gunung Agung on Bali breaking through the clouds in the distance.

Day 3 (2000Hm down, 3h 10min)

This is a hard day, because we did two days before, and because I have a problem with a blister on my foot; 2000m down is not my preferred hobby. While the 1st part is on loose scree, almost all the trail is in a dense jungle, with 1000s of roots to be jumped over. We meet dozens of trekkers and porters and guides who climb from this side. The youngsters run down and take only 2.5h for the 5km, 2000m vertical! We are fast, and are in Senaru HQ 600m at 11am. We take a shower, get transport back to Bangsal harbour where we have lunch, wait for 2h until the local boat fills up and takes us back to Gili Air.