Merapi

merapi (+/- 2900 m) is one of the most active volcano in the world. it's dangerous, but also one of most beautiful place in yogyakarta. you can enjoy a lot of adventure activity here, like hiking, rock climbing, bird watching, camping, etc. there's also a lot of cultural attraction too. merapi is a place where myth and supernatural stuff still strongly belief by the javanese specially who live around merapi. even the eruption is considered as a gift, not disaster. it has strong connection with keraton Sultan, king of Jogjakarta.
you want something adventorous? you can get it there, it's a beautiful mountain.
you want something cultural? you'll get it. there's Ulen Sentalu, a beautiful Jawa museum in Kaliurang, in southern Merapi, villages with strong Javanese culture, good Javanese food (find Jadah Tempe Bacem if u're there), and of course, interesting story myth.

Along with Mt Bromo, this is one of the best active volcanoes to get up close to in Indonesia without too much effort, (compared to Gunung Rinjani in Lombok!). The night we were there it was erupting great fireballs of molten rock and lava down it's slopes, which was awe inspiring. Make sure you take a jacket as it gets pretty cold up there, and if you're into photography, bring a tripod for your camera. People who like adventure and hiking will definitely love to climb it. The sunrise is so beautiful there. To be able to see the sunrise you need to start at midnight as it needs 4-5 hours to climb. Be prepared! Bring a jacket, shoes and torch. You will need food and water, but you can buy before climbing the Merapi.
How to get there?
1. From Jogja: Take bus towards Magelang. Stop at Mungkid (Mungkid is between Jogja and Magelang) and take a mini van (yellow ones) to Selo. Please ask local guides to guide you climbing the Merapi after you arrive at Selo. You need to pay around Rp. 250.000,- per guide.
2. Ask your hotel to arrange the trip.
3. Take the tour to Merapi when as there are many.

Directions: Jogja-Mungkid-Selo-Merapi. The safest route is from Selo. Selo means gap in Javanese language. Selo is a village located between Mount Merapi and Mount Merbabu.Source
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