Nguom Ngao Cave is a large limestone cave near Ban Gioc-Detian Falls, with chambers of stalactites, stalagmites, and sculpted rock formations. It is one of the strongest side trips in the waterfall area and can be visited before or after the falls.
The cave is especially atmospheric in quieter periods, when the echoing chambers feel far removed from the busier viewpoints outside. Bring shoes with decent grip, since cave paths can be damp.