Pantai Karangbolong, Coastal beach in Kebumen, Indonesia

Pantai Karangbolong is a gently sloping, wide grey-sand beach in Karangbolong village, Buayan district, Kebumen regency, Central Java. It is backed by hills of clastic sedimentary rock derived from volcanic breccia of the Gabon formation, about 30 to 15 million years old. At the eastern side lies Gua Karangbolong, a 30-metre-long, 10-metre-wide and 5-metre-high cave formed in fractured lahar breccia.

The cliff at Pantai Karangbolong is breccia of the Gabon formation, a volcaniclastic rock exposed together with sandstone and claystone layers and dated to the Oligo-Miosen, roughly 30 to 15 million years ago. The cave beside the beach formed by collapse along the boundary between the breccia and the softer sandstone or claystone beds; blocks hanging from the roof kept falling under their own weight, enlarging the hole, helped by joints that weakened the bond between rock components. Small collapses of this kind can still be seen at the cave's eastern and southern ends.

The name Karangbolong is Javanese for "hollow rock", after the cave in the eastern cliff. The beach's swiftlet nests are harvested and managed by the local government as a source of regional revenue, a use visitors can ask about in Karangbolong village.

The beach is in the Buayan district and is most easily reached by private vehicle from Kebumen, with parking available close to the shore. The southern coast here can have strong currents, so it is worth staying close to the shoreline and checking sea conditions before going in the water.

Gua Karangbolong, on the eastern side of the beach, is a 30-metre-long, 10-metre-wide and about 5-metre-high passage formed in lahar breccia of the Gabon formation, exposed with sandstone and claystone layers. Because it is not a limestone cave, it holds no stalactites or other ornaments; its collapse along bedding planes is best seen at the cave's eastern and southern ends.