Located 3 km southeast of Trong Mai Islet lies Bo Nau or Pelican Cave, one of the most beautiful caves in Ha Long Bay. The name Bo Nau is associated with the fact that pelicans often take shelter here.
This vaulted grotto covers 200 square m. The floor of the grotto is wide and flat, but not deep, and its wall features lots of stalactites and stalagmites.
Turning southward, Bo Nau Cave enjoys cool wind. Standing there, one can hear the murmur of the sea throughout the year.