There are many caves and grottoes distributed throughout the stone islands of Hạ Long Bay. The most famous are concentrated in the central zone of the World Heritage area, such as: Thiên Cung (Heavenly Palace Grotto), Ðâu Gỗ (Driftwood Grotto), Sửng Sôt (Surprise Grotto), Bồ Nâu (Pelican Grotto) and Ba Hầm (Three Shelter Lake). There are also other caves and grottoes situated far from Ha Long’s coast, such as: Tiên Ông, Hang Hanh and Soi Nhu.

The formation developed through various forms of erosion over thousands of years. There are still many sealed caves and grottoes, formed in the carbonate mountains but not yet having an entrance. Eventually, they will be discovered through the effects of nature or man