Last updated: July 16, 2026

Bioluminescent plankton is a natural glow that lights up in the water when disturbed by a paddle stroke or a fish swimming past. In Lan Ha Bay near Cat Ba, night kayak tours reach dark, sheltered lagoons where the glow is easiest to see.

Pick Lan Ha Bay if you want postcard karsts without the crowds. Pick Halong Bay if you want Vietnam's most famous name and don't mind sharing the water. Both bays sit in the same UNESCO-protected seascape, but they feel different on the water. Picking the wrong one can shape your whole north Vietnam itinerary.