Cayo Iguana is a tiny offshore islet north-west of Cayo Largo, named for the colony of large native rock iguanas that lives on it. Boats from the Cayo Largo marina run a half-day excursion that combines a snorkel stop on the reef with a landing on the islet, where the iguanas wander unconcerned among the sea grapes and palms.
The snorkelling along the way is decent — clear shallow water over a sand-and-coral bottom. The islet itself is small enough to walk across in ten minutes. Bring sun protection: there is essentially no shade.