Jomblang Cave

Jomblang is a sinkhole in the karst hills of Gunungkidul, formed when the roof of a cave system collapsed. Visitors are lowered about sixty metres down the shaft on a rope and pulley worked by a team at the top, landing in a patch of old forest that has grown on the floor of the hole where the light reaches. From there a slippery passage leads through to a second shaft, Grubug, where at the right time of day a single beam of sunlight comes down through the opening and lands on the rocks and the underground stream. That beam is the reason almost everyone comes, and it only appears around midday.

What you actually see

• The rope descent - being lowered down the vertical shaft in a harness by a hauling team.
• The forest floor - the patch of ancient vegetation growing at the bottom of the sinkhole.
• The Grubug light beam - the column of sunlight falling through the second shaft around midday.
• The underground river - the stream running through the chamber below the beam.

When to go

The light beam depends on sun, so aim for a clear day between April and October and a slot around midday. In the wet season the shaft can flood and trips are cancelled outright. Numbers are capped and slots sell out, so book ahead rather than turning up. Allow a full morning including the drive.

Honest expectations

There is a lot of waiting: groups queue at the top for their turn on the rope, and the whole thing can take hours for maybe twenty minutes at the beam. The floor is deep mud and bat guano, and you will be filthy. Cloud means no beam and no refund. Anyone uneasy with heights or confined descents should skip it.

Nearby

The Gunungkidul beaches and the Pindul cave tubing river are close by.