Informally called the Indochine Cave ever since the film starring Catherine Deneuve was shot here, this short grotto leads to a hollowed island lagoon with steep walls of jungle surrounding shallow salty waters. On budget trips to Cat Ba Island, boats stop at the entrance and small shuttle boats will take you to the cave through low openings. The cost is 20,000 VND for the short ride, but the proceeds allegedly go to help the small floating school in the nearby floating village (you pass the school on the way).