Behind Luengoni Beach, the limestone opens into a network of underground caves with clear freshwater pools inside. The caves are hidden in thick vegetation and require a local guide to visit — arrangements can usually be made through accommodation or in the village. The combination of swimming in dark, cool cave water and then emerging onto one of Lifou's best beaches is hard to beat.
Bring a torch and shoes you don't mind getting wet. Trips typically last an hour or two and finish on the beach.