The freshwater Cueva de Saturno, 1km south of the Vía Blanca by the road to Varadero's international airport, is a highly popular (ie crowded) subterranean cave with a pool billed as a snorkeling and/or swimming spot. The water's about 20°C and the maximum depth is 22m, though there are shallower parts. There's a snack bar and equipment rental post on-site.
Arrive early if you want to avoid the Varadero tour groups.
