Cayo Largo del Sur is a small limestone island off the south coast of Cuba formed over millions of years from the remains of marine organisms.

The cay is about 25 km long and 3 km wide and is the second largest island in the Canarreos Archipelago. Cayo Largo del Sur is part of the special municipality of Isla de la Juventud.

Pristine beaches, clear waters that reveal the underlying ocean floor, scuba diving, and wildlife draw tourists to the island. There are several all-inclusive resort hotels but no people live there permanently. Domestic and internationals flights serve the island. A large catamaran style ferry provides surface transportation.

Major tourist attractions of Cayo Largo are the west beaches, Playa Sirena, and Playa Paraíso. These beaches are a kilometer apart, and one may easily walk between them when the tide is not full. A shuttle "train" service takes tourists from the resorts to these beaches. Playa Paraíso offers one of the finest undeveloped beaches in the world. Other attractions are water sports related to the hotels, dolphins, and docks for catamaran trips.

The island has a large variety of animal species such as turtles, gulls, and pelicans. Visitors can easily view many very large starfish and other tropical fishes that congregate in the lee side of the beaches. Living coral reefs are one more attraction for tourists on this island.

Cayo Largo tolerates nudism in some areas on the periphery of the resorts.