Bat Islands

A Bat Islands trip is a full day out and operators sell it that way. Boats leave Playas del Coco early, run north along the dry Santa Elena coast and normally fit two dives in before turning for home, so nobody is back for an afternoon reef dive. The islands sit inside a national park sector, so there are park fees to cover, and most shops need a minimum number of divers to launch, which is why trips run on set days rather than on demand. A hard blow can still cancel one at the dock.

Above water the islands are dry, sun-baked rock carrying thin tropical dry forest, and the diving underneath matches. Expect volcanic boulder slopes, ledges, cracks and sand channels rather than a coral reef. Growth on the rock is low and encrusting, so what holds attention is the shape of the terrain and whatever swims past it. Site choice is made on the morning by how much water is moving, and the same rock can be an easy drift one day and a hard push the next.

Briefings here are more specific than most divers are used to: a quick negative entry, a tight group, no chasing, no fanning out, everyone up together. Cold layers arrive with little warning under a surface that can sit close to 29°C, which is why regulars carry a hood and more neoprene than Guanacaste sunshine suggests. Between the chill, the depth and the surge, dives here tend to end early rather than on a low tank, so plan the day around two rather than three.

It suits divers already comfortable working in current who are basing themselves in Guanacaste for a week, with the shorter runs out to the Catalina Islands as a warm-up and this as the one big day. May through October is the stretch worth planning a trip around, and July and August are the most reliable weeks inside it. The windy first months of the year still dive when the sea allows, but the odds tilt away from the encounter most people booked for.