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 Yogya on Jl. Magelang for 45 min. When you reach Mungkid turn right onto Jalan Boyolali - Mungkid and head towards Ketep. At Ketep turn right and continue following the Jalan Bololali - Mungkid 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.
Another way is to take bus to Magelang from Jombor Terminal in Yogyakarta, get off at Blabak (Mungkid) and take ojek to Selo (approx. 1.5h bumpy ride, Rp 80k). Make sure to arrive to Blabak early enough to reach Selo before sunset. Although riding motorbike during the night is possible, it is very risky given quality of the road and you may have trouble finding volunteers to drive you even for higher price. Do mind that green Bemos don't go directly to Selo (locals say the road is too bad).
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!
[April 2016] The climb from Pasar Bubrah to the top of Mt. Merapi is officially closed. Since nobody enforces it in practice tourists and guides climb with no restrictions. Do mind however that reaching the top, besides being illegal, is more risky than usual.
There is a ticket booth before NewSelo where you'll be asked to pay a whopping 150 000 rps/person to climb Merapi. You can not avoid the mafia guys there if you come with a driver because a guy at Selo will call them to let them know that you're coming. If you don't want to buy a ticket you have to take a guide which costs 300 000rps for 3 people. Don't try to argue much with the big guy about how he 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 in the mafia or he'll try to punch you). Best thing to do is to avoid Merapi or try to snake on foot at night. The true regulation, you must pay for a ticket for RP.150.000(insurance is included). Taking a guide is optional, but climbing with a guide is recommended because the guide knows when it is a safe time to climb Merapi.
A guide is recommended, esp. until the camp at Pasar Bubrah, because most of the trail is in the forest or surrounded by bushes limiting your ability to see other tourists flashlights above you. If you are thinking about following guided groups think twice. The guides are well organized, have radio communication and are aware of such tourists. They will kindly ask you to go first, especially just before the trail forks. It is ok to go without a guide but allow yourself more time to account for navigation mistakes.
At the top besides the crater you'll find monitoring stations and small concrete viewing platform, were most climbers meet and wait until the sunrise. 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 hundred 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.
Depending on the state of volcanic activity you may be able to witness molten lava flows way down the slopes of the mountain.
This trail is not for the light hearted. There is a clear route up Mt Merapi leaving just north of a Museum of sorts (Dusun Kinahrejo Rumah Mbah Marijan on google maps). This route will not get you to the highest peak but instead a slightly lower peak on the southern edge of the rim. Here the channel carved out by lava on one side and vertical walls on the other prevent you from making it around the rim to the highest point. The sunrise can still be viewed from this point and great views of the crater, lava flow channel and out over Yogyakarta can be had. As mentioned above this route is officially closed due to it being too dangerous a statement which rings true particularly after venturing above the tree line where unstable rocks and angles exceeding 50 degrees made climbing very treacherous. Rocks which come loose under foot above the tree line will not stop on their way down and easily reach lethal speeds as they gain momentum. Although it is unlikely to come across other climbers on this route be very wary if you do find yourself below others in the rocky and extremely steep section above the tree line. Also consider falling rocks if climbing in a group. Signs put up by the Grama Buana Mountaineering Club mark the route at various locations, most usefully above the tree line where defined tracks don't exist, which are all dated 26/3/2016.
From the unmarked start of the climb you will follow a quite wide walk trail which ends at a concrete set of stairs and some simply made shelters. Here the trail narrows significantly but is still well defined. A second set of stairs will mark a nice lookout over Jogja followed soon by a Weather station. A second weather station will then be shortly followed by a section which has had recent land slides on either side. In June 2016 it was easy to cross the narrow ridge made by the land slides but due to the sandy soil in this section it may well of changed given another wet season or two. The next point of interest is a rocky view point which gives even better views over Jogja and is a great stop for a rest. From here the trail gets considerably steeper. The end of the tree line can be found next. This section is not for the light hearted. Follow the arrows and flags left by Grama Buana and watch your step. Rocks are often loose and the gravelly sand offers little to no traction. The climb is extremely steep and a slip could see you rolling all the way to the tree line, a fall you would not survive. Double check each rock for stability before committing your full weight on each one and watch for falling rocks from above. You will eventually reach the peak right next to an extremely deep valley carved out by lava. As mentioned above the summit on the other side of the lava flow is inaccessible using this route but the view is absolutely stunning. Descend the same way you you came up and again watch each step as you go. Descending the treeless section of the climb is harder than going up, take your time, but the rest is pretty straight forward.
See map Here for June 2016 route described above
The climb took a single climber 14 hours summiting for sunrise. The route from the start to the waypoint marked "much more defined track" was hacking through the jungle sort of stuff... very slow going.
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.
Ticket foreign: IDR 150.000
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. Event, difficult to find shops on the night. 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) .