After three major eruptions 3,500 years ago that created a caldera measuring 22 by 25 kilometers, the Ijen volcano rose to world fame for its crater lake with the most acidic water in the globe.
Against the risk: Mining activities are seen in the famous Ijen crater in Bondowoso, East Java. The Ijen volcano rose to world fame for its crater lake with the most acidic water in the globe. JP/Indra HarsaputraLooming behind the natural beauty and geothermal energy potential of the Ijen crater or Kawah Ijen, however, is a threat to millions of people settling around the East Java volcano.

Stefannie, 35, a French tourist, snacked on a small dish of locally grown macadamia nuts while she finished her cup of luwak coffee — made of beans fermented in civets’ bowels — before setting out from the Arabica Homestay.

“I’ve got to rush to the Ijen crater to watch the rising ...