Grotta Gigante (Giant Cave) is a cave located near the city of Trieste, in northeastern Italy. The cave is known for its enormous size, with a volume of around 350,000 cubic meters, making it one of the largest show caves in the world. The cave was discovered in 1840 by a local blacksmith, and has since become a popular tourist destination.

The cave's main chamber is about 107 meters long, 62 meters wide, and 98 meters tall, which is large enough to contain the entire nave of St. Peter's Basilica in Rome. Visitors can take a guided tour through the cave, which takes about an hour and covers a distance of about 1 kilometer. Along the way, visitors can see various stalactites, stalagmites, and other limestone formations, as well as an underground lake.

The cave is also known for its remarkable acoustics, which have made it a popular venue for concerts and other performances. The cave's main chamber can accommodate an audience of up to 500 people, and a number of famous musicians and performers have performed there over the years.

In addition to the cave itself, there is also a small museum at the site, which contains exhibits on the cave's history, geology, and biology. The museum also features a display of prehistoric artifacts found in the cave, including bones and stone tools from Neolithic and Bronze Age human settlements.