Once you arrive at Kaliadem, the last village on the road up to Mt Merapi, there are many different Jeep operators who can take you further up the volcano and into the lava fields. Our driver recommended one operator called MJLC (Merapi Jeep Land Cruiser) who were excellent. Our Jeep driver / guide was a young(ish) guy who spoke reasonable English, was very friendly and knowledgeable about the area. He was also a skilled off road driver. Before starting the Jeep Tour you need to choose between the Short (1 1/2 hours), medium (3 hrs) or long (4 hrs) tours, There is also a sunrise tour option. We decided on the short tour which took us to all the main attractions except for driving through the Kali River. Our tour cost IDR 300,000 (US$ 20) for the Jeep and guide / driver and visited the Museum, Alien Rock and the Kaliadem Bunker.
Mt Merapi is actually one of the worlds most active volcanoes, it last erupted in Nov 2010 with a massive eruption which left a huge scar on its cone and unfortunately resulted in 353 deaths as many pyroclastic flows (included hot gasses) cascaded down its heavily populated flanks (a total of 350,000 people were evacuated). The resultant ash cloud caused severe aviation disruption (something I remember), with ash also falling on Jogjakarta city 30 km away. Ash fall also caused severe damage to the ancient Borobudur Temple some 28km SW of the volcano resulting in a major cleaning project which caused the temple to be closed to visitors for about a year.
The first stop on the Jeep Tour was the small museum dedicated to the Nov 2010 eruption. Many villages were destroyed by the eruption, the museum is situated in the buildings of one of the destroyed villages (left as it was after the eruption) and consists of destroyed artefacts and many photographs of the eruption and information panels explaining the eruption timeline.
The second stop was the Alien Stone (a large lava boulder exploded from the volcano which resembles an alien face). This stop has excellent views of the volcano and the ugly scar which was the result of the Nov 2010 mega eruption, although in truth when we visited it was quite cloudy which effected the view of the volcano.
The third and last stop was the Kaliadem Bunker, the highest point of the tour. This bunker had been built to provide the local population with a refuge point from pyroclastic lava bombs during previous eruptions. During the Nov 2010 eruption unfortunately the lava flows descending the flanks of the volcano completely encased the bunker killing those inside (two people). You can enter the bunker, but in many ways it is a sad place given what happened.
Be warned the roads are seriously bumpy, but that was half the fun. Drinks, food and souvenirs were available at all the stops although the Bunker had the biggest selection of outlets. One and a half hours was ample time to do the tour, it was not rushed with ample time to wander around the places visited. The roads get quite dusty so face masks are provided free of charge.
A great experience and highly recommended.