Going underground, expedition members enter Hang En, a cave tunneled out by the Rao Thuong River. Dwindling to a series of ponds during the dry months, the river can rise almost 300 feet (91 meters) during the flood season, covering the rocks where cavers stand. Photograph by Carsten Peter
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Going underground, expedition members enter Hang En, a cave tunneled out by the Rao Thuong River. Dwindling to a series of ponds during the dry months, the river can rise almost 300 feet (91 meters) during the flood season, covering the rocks where cavers stand.

Photograph by Carsten Peter