Literally "Mountain of Fire", Mount Merapi is the most active volcano in all Indonesia — no mean feat — and it has erupted at least 68 times since 1548. The volcano is thought to be largely responsible for the downfall of the Hindu Mataram kingdom in 1006 and the desertion of the huge temple complex at nearby Prambanan. Recent eruptions include 1994 (64 killed), 2006 (no immediate deaths, but a prelude to an earthquake that killed over 5000) and 2010 (30 dead).
Anyone thinking of climbing the mountain must first check if it is safe to do so. While climbing the mountain with a qualified guide is recommended it is not necessary or mandatory, as the track to the summit is wide and clearly marked. But this is not the case at night. Many routes are invisible since visibility is low as it's dangerous.
Selo is the last village on your way to Merapi. A taxi from Yogyakarta airport to Selo and back will cost you around Rp 1,000,000. Most of the drivers will happily wait for you while you climb Merapi and will take you back to your hotel.
Alternatively you can hire a scooter in Yogyakarta and ride out to the summit. Ride north out of Yojya on Jl. Magelang for 45 min. When you reach Mungkid turn right onto Jalan Bololali - Mungkad and head towards Ketep. At Ketep turn right and continue following the Jalan Bololali - Mungkad into Selo. From Selo ride up the steep road (on the right as you come into Selo) to the trail entrance where you can leave your scooter.
There are a few ojeks (motorcycle taxis) offering informal transport around the area.
In the villages around the base of Merapi, almost any vehicle you see on the road is a potential lift (for cash), so don't be shy!
[October 2015] There is a ticket booth before NewSelo where you'll be asking to pay a wooping 150 000 rps/person to climb the Merapi. You can not avoid the mafia guys here if you come with a driver because a guy at Selo will call them to tell that you're coming. If you don't want to buy a ticket you have to take a guide wich cost 300 000rps for 3 people. Don't try to argue much with the big guy how speaks english : He is the leader and a very aggressive fellow if he feels that you won't be part of their mafia and you're not willing to pay the ticket (PS: don't tell the guy he's mafia or he'll try to punch you. Best thing to do is to avoid the Merapi (it really doesn't worth 150 000rps) or try to snake on foot at night. Do avoid the rainy season which spans Late October to Early April. The slopes become slippery and the high altitude, night climate and rain makes the hike unbearably cold, especially if you are waiting for the rain to pass at one of a handful of sheds on the route up. Waterproof winter wear is necessary if you intend to brave the rains in these months and especially at night. The rainy season also means cloudy days and reduces the prospects of viewing any sunrise. Do pack a set of dry clothes to change into, since you are bound to get wet, and good hiking shoes with sufficient friction to mitigate the wet roads. The trip to base camp by car can also get hazardous as fog builds up after a downpour and visibility degrades to less than 1m. Trekking on and around Merapi is a popular activity (at least when the volcano isn't spewing out hot gas and ash). From Selo, the nearest village on the north slope, it is 3 hr hike to the summit for the fit and healthy. For others it will take 4+ hr to climb, and nearly the same time to get back down again. Carry a small pack with some food, a good flash light, with spare batteries (available for purchase in Selo village), and at least 2 litres of water per person. The track to the top is a reasonable grade and is mostly the mountain's natural water drains, a guide is recommended, can get muddy and slippery when it rains. Once through the tree line the track is less defined and the final climb to the summit (after the memorial plaque) is a very steep scramble over loose and broken rock. While not in itself dangerous, do take your time on the last section. There is a 200m section of ash which is the hardest once surpassed the rocky section to the summit is reasonably steep but is like any other for regular hikers. Most climbers start at about 1AM to be sure of reaching the summit by sunrise at 5.30AM. Night climbing is wise in any case, as the upper reaches of the mountain are completely treeless and the sun can fry you to a crisp. The sunrise views across East Java are quite stunning. The way back can be more tricky that the rise, since the ash and the inclination of the route, make it almost impossible to stand up, so pay particular attention.
There is an alternative route from Kinahrejo at the south side of the mountain. This route is currently forbidden, because considered to be too dangerous. So if you decide to go this way, you do it at your own risk. Starting from Yogyakarta one gets there by taking a public bus to Kaliurang (spelled on the bus as "X Urang") to the last stop. From there you can pay an ojek for an exorbitant 50.000 Rp. (7km) to Kinahrejo but hitching is more fun. There are several cheap places to stay there. The trail starts at the lava stream 200m east of the memorial museum. Follow the lava stream. Make sure you start early (< 7 0' clock) because there might be some officials that don't want you to go there. Walking up you might encounter some locals that will tell you not to use dirty language and ask for forgiveness if you pee. This to make sure you won't upset the volcano. After a few km, you arrive at a beautiful viewpoint of Mt Merapi. Fromt there follow the rocky river at your left. After a few hundered meter you will find a trail that successively leads to a portal, a place of offering and 2 weather stadions. Once the trees stop it is pretty straight forward but not easy. Mt. Merapi is basically a pile of rubble. 3 steps up, slide 1 down. Walking up should take about 5,5 hrs. walking down a bit less. Bring 3 liter of water.
The less active should not feel left out as there are far less strenuous treks around the base of the mountain. Ask around in Selo.
Depending on the state of volcanic activity you may be able to witness molten lava flows way down the slopes of the mountain. Take local advice:
A signboard at the entrance of the Merapi Plateau reads: "Leave nothing but tracks, carry nothing but photographs"
Not many options to eat exist in or around Selo. Local food stalls offer basic tea and local food items. Plenty of such stalls can be found in Selo.
Nothing except the local stuff. Carry your own bottles.
There are no explicit rules which prohibit camping on and around the mountain. You will need to bring in all your own equipment and you must keep yourself fully briefed with the latest safety reports. Also make sure you bring in enough water, as the springs and streams on the mountain are very sulphurous.
It is hard to think of many more dangerous volcanoes anywhere in the world. Always heed local advice from a guide, and it pays to check the bulletins at the Smithsonian Global Vulcansim Program and the Indonesian Geological Survey (in Indonesian) .