Halong Bay’s limestone islands are dotted with caves of all sizes and shapes. Most of these are accessible only by chaerter boat, but some can easily be visited on tour. The most famous and beautiful caves in Halong bay are Sung Sot cave (Amazing cave), Thien Cung cave (Heaven chamber cave), Dau Go cave (Drift wood cave), Trinh Nu cave, Bo Nau cave… and many other cave that lies in Bai Tu Long bay and Lan Ha bay wich is beside Halong bay.
Some 2-3 km southeast of Trong Mai Islet lies Bo Nau Cave or Pelican Cave. This vaulted grotto covers 200 m2. The floor of the grotto is wide and flat, but not deep, and its wall features lots ofstalactites and stalagmites.
At the entrance are three stones, looking like three fairies with their heads close to one another. Two men appear to be playing chess,with the third serving as a referee.
The name Bo Nau or Bo Nong is associated with the fact that pelicans often take shelter here. If Dau Go Cave lies completely inside the island, Bo Nau opens its mouth at the side of the island. Stalactites fall down from the roof of the grotto in different clusters. Meanwhile stalagmites grow up in different shapes and layers. Is this that the life out there is so noisy that the three fairies have to choose this tranquil place to play chess? Turning southward, Bo Nau Cave enjoys cool wind. Standing there, one can hear the murmur of the sea all year round.