Located east of Cat Ba Island and at the edge of Halong Bay, Dark & Light Cave is actually a system made up of two separate caves, hence the name. The Dark Cave stretches for 100 meters and has very little natural or artificial light so you’ll have to bring a flashlight. The cave commences at the water level of a distinctive arched entrance that leads to a huge lake with massive trees and a variety of exotic orchids. This is definitely one of the best places to hone your kayaking.

Cat Ba's beautiful national park is home to 32 species of mammal, including most of the world's 65 remaining golden-headed langurs, the world's most endangered primate. There are some good hiking trails here, including a two-hour return trip to Ngu Lam peak and a day-long hike to Viet Hai village. Of the mammals present in the park, the more commonly seen include macaques, deer, civets and several species of squirrel, including the giant black squirrel. Seventy bird species have been spotted here, including hawks, hornbills and cuckoos.

Stretching for about 300 meters, this is one of the most remarkable caves in Cat Ba Island and certainly one of the top Halong Bay attractions. Venturing inside is like stepping into nature’s wonderland, thanks to the thousands of sparkling stalactites that take on different shapes and forms.