Halong Bay boasts a stupendously diverse ecosystem comprising evergreen tropical and marine biospheres. Snorkelling in Halong Bay’s warm, shallow ocean allows travellers to explore 120 hectares of colourful coral reefs with 80 species of fishes and turtles and underwater caves. Cong Do Island, Monkey Island, Van Gio Island, Cat Ba Island, and Trai Cave are the best snorkelling spots here. Gear rentals cost around VND 300,000.