A Hot and Steamy Taste of Java

I'm choking on smoke: the hills steam, the ground boils. Such turbulence might seem par for the course on any highland hike in Indonesia, which has more active volcanoes than any other nation. Yet the footing is especially treacherous in Java's Dieng Plateau, a largely forgotten ancient capital steeped not only in thick mist but immense mystery.

Dieng was a holy city with at least 400 temples, including some of the island's oldest Hindu ones, dating to the 8th century. But like magnificent Borobudur nearby, Dieng was built and then rapidly abandoned. Historians have long...