The Dark and Light grotto is not the only beautiful caves in Halong Bay, but it is the perfect combination of lime-stone mountains and sea makes a unique site to visit.

Closed to the Bai Tu Long Bay and Lan Ha Bay, an enclosed group of islands create the caves. At the water-level, an arched entrance leads to the grotto, just at the base of the island. Passing through the pretty entrance, you come across a tranquil round lake, surrounded by luxuriant trees and high dangerous stone walls.  A see-lake is formed by the imposing islands sheltered from the blows of sea wind and only connected with the sea through a 4 meter wide, 100 meter long, and 3 meter high mouth. On the cliff one still find traces of fossils of fresh-water snails, which prove that it was a human habitat in the past and must have been a deep valley then. The Dark and Light cave is not too far from Surprise Cave area around 2km. The system of islets are really imposing. 

Exploring dark and bright cave, the best way is doing kayaking and swimming through the tunnel. The Dark Cave is the long and dark, which will require a torch to be handed for you beforehand. The Light Cave is short, and you can see the other bright side from this side.
Long and short, dark and light. That made The Dark and Light grotto.