Bonaire's limestone is full of caves, and this tour gets you into two of them. You swim through a water-filled cave, try a short freedive, then climb into a dry one. Private groups of up to seven can book the tour for themselves.
It meets on Kaya Barcadera, which the map services do not place, so the pin is on Kralendijk. It shares a phone number with the Mangrove Center.