The cave known as Grotta Gigante, meaning Giant Cave, lives up to its name. The main cavity is about 130 meters (427 feet) long, 65m (213 feet) high and 107m (351 feet) tall, for a total volume of about 600 thousand cubic meters. Although it is not the largest known natural cavity, it is the only cave of its size that can be visited without the need of speleological equipment and training.

The first modern exploration was begun in 1840 by A.F. Linder who was looking for the subterranean course of river Timavo. By 1905 the cave was opened for tourists and a system of walkways was installed and the cave lighted by thousands of candles. Since the fifties the cave has been illuminated with electric lights and safer walkways were built during the seventies.

Currently it is open to public throughout the year, although only guided tours at fixed times are possible. The internal temperature is constant at 11°C (50°F) and the humidity is quite high (90%), hence it is a good idea to take a sweater if you plan a visit during summer months.