Bassin Bleu is four pools of cold blue water let into a limestone gorge above Jacmel, on Haiti's south coast, and each one is harder to reach than the last. The colour is the spring's doing. Rain sinks into the hills, dissolves the limestone slowly and comes back out carrying what it took, which turns the water cobalt instead of the green of an ordinary stream. It is also what can be lost: runoff off the bare slopes carries more silt than the spring can dilute, so after a storm the basins go brown until it settles. The colour is at its strongest in the dry weeks of January and February.
The walk in climbs above the canyon first, and the hills open on a valley of coconut palms falling to the Caribbean, Jacmel's bay a pale line at the end. Then the path drops. The first pools are the easy ones, ringed by rock shelves that the guides use as diving boards without ceremony. Depths run from under three metres to well over twenty, and from a ledge they all look much the same, so which basin is which gets asked before anyone jumps. The last one has no way in on foot. You go down a short vertical face hand over hand on a rope, with a guide from the village anchoring it below you, and the gorge closes overhead. Then the water turns cobalt. A single waterfall comes about ten metres into it, ferns hang from the walls all round, and the noise fills the gorge around you. The water under the fall is cold, clear and far over your head. Local belief puts water spirits in that pool, each of them named: the bisimbi, guardians of springs and fresh water, carried here from Central Africa, and La Sirène among them. Cold, shaded water with no bottom in sight is exactly the kind of place they are said to hold.