Dieng Plateau of Java: central attractions

Located more or less in the geographic center of Java, and mostly overlooked by travelers, is a high plateau of Dieng. The plateau is quite different from the usual high-altitude plains: it is comprised of tectonic folds stuck together, dotted with maars, geysers and volcanic cones, It's alive with seismic activity, it breathes sulfur. "Dieng" derives from old Javanese for "abode of gods" - romantic types may try and see divine presence in the exceptionally beautiful landscapes, those with mystical inclination - in the incessant geothermal activity, and the down-to-earth ones - in ancient temples standing here and there on the plateau. For a traveler, its attractions are mainly of volcanic origin: colored and boiling lakes, deep craters, and gorgeous views from the numerous peaks.

Hindu temples

There are a number of Hindu temples in Dieng, built presumably around 7th-8th century CE. This puts them among the oldest buildings in Java. All of them are ruined to some extent, but most still retain their religious significance. For tourists, the most popular temple group is Arjuna complex. The main structure here has survived to erosion of time better than the rest. Only the roof collapsed, but has been reconstructed. 

A large festival fusing traditional rituals with tourist shows takes place here in August. One of the highlights is Ruwatan Anak Gimbal ceremony: boys born with natural dreadlocks (or so it is believed) are shaved to return their magical hair to the gods. Bima temple, right in the village of Dieng, is interesting in the way it's integrated into the otherwise Muslim community. On auspicious dates, one may chance upon a Kejawen (Javanese Indoanimist) ceremony here.

Sikunir Hill

Aside from the temples, perhaps the most famous spot in Dieng is Sikunir Hill - a viewpoint on the summit of a dormant volcanic cone. While the famous sunrise view from there is good, it's by far not the best in the area. The real reasons behind the popularity of Sikunir is human laziness (there's a motorable road almost all the way to the top). Nearby Mt. Bismo, for example, is taller and offers better panoramas - but it has to be climbed on foot. And the best view in Dieng, doubtlessly, is from its highest peak: Mt. Prau but it takes even longer to climb. 

Telaga Warna

Another famous sight in Dieng is Telaga Warna - "Colored Lake". Magmatic minerals turn the water of this lake into liquid emerald. The usual rule of visiting tourist hotspots applies: enter from the back. Partly, because a hefty entrance fee is charged at the official gate, with two-tier pricing (foreigners pay ~10 times more). Partly, because the coastline next to the gate has been "developed", that is, transformed into a rather unattractive recreational zone. And partly, because the best view of Telaga Warna is from the mountain range behind it - another, more olive-coloured lake is visible from here, and the Yin-Yang-like balance of the two is gorgeous.

Practicalilties

Getting to Dieng Plateau is simple - a reasonably good road served by regular buses connects it with Wonosobo on the old Trans-Javanese highway, which is turn well connected to most destinations in Central Java. Accommodation is mostly in homestays or simple guesthouses; or else, camping out. A few villas are on offer for the wealthier travelers. In August, when, in addition to the festival, frost sometimes forms at night on Mt. Prau, local tourists fill the available accommodation, and prices triple.  

Keep in mind that night temperatures in Dieng are extremely low for equatorial Indonesia - bring more layers than you think you'll need. Some of the attractions have an entrance fee, and it's inevitably much higher for foreigners than for locals - take it, leave it, or sneak in from behind.