The Trinh Nu Grotto or Virgin Grotto is situated on the island range of Bo Hon in the system comprising the Sung Sot Grotto, Ðong Tien Lake and Luon Grotto. It is about 14km from Bai Chay Tourist Wharf to its southeast. For fishermen, the Virgin Grotto is their house, but for young lovers, it is considered as the symbol of truly love, and is the romantic place for taking oath of love.

A trip to Cat Ba Island can do separately or in combination with a visit to Halong Bay. Cat Ba Island is the largest island in the Cat Ba Archipelago that consists of 350 limestone outcrops adjacent to Halong Bay.

It is situated on the south-west side the bay, 4 km from the wharf outside of Ha Long City. The way to Thiên Cung is a perilous one, covered on both sides by thick forest. After entering a narrow gate, the grotto’s 130-meter-long girth opens up.