You can go there just for one day because it's a small island but a chill out one though. You can visit the lighthouse and from the top you've got an amazing view of the lagoon (before entering you need to go at the boutique and get some entry tickets). You can go on a see through boat as well but it doesn't take you very far away so you can also go with your sorkel instead take some bread with you if you want to feed the fish. Warning for people scared of snakes, this island is full of "tricots raillés" which are striped snakes hidden in trees or under the boutique terrace they don't attack you though.