Grotta Gigante

Grotta Gigante is a single colossal chamber hidden beneath the limestone plateau behind Trieste: a hall so tall that a church tower would fit inside with room to spare. A laser survey carried out in 2011 measured the Great Cavern at about 98.5 metres high, 167.6 metres long and 76.3 metres wide, a volume of some 365,000 cubic metres, and in 1995 it entered the Guinness Book of Records as the largest show cave in the world, a title it held until a larger chamber in France opened to visitors in 2010.

The cave is the surviving stretch of an ancient river gallery cut into Upper Cretaceous limestone that is full of fossil rudists, shellfish that died out with the dinosaurs. Water abandoned it at least five million years ago; a huge collapse, dated to roughly half a million years ago, then merged a lower and an upper gallery into the vast space seen today. Since then dripping water has built stalagmites and columns, some of them stacked like piles of plates because the drops fall from up to 80 metres and splash calcite over a wide area. Iron oxides streak the white and grey calcite with red. A visitor route of 850 metres descends by long flights of steps to 101 metres below the surface, crosses the Great Cavern and climbs to a viewpoint where the vault is almost within reach and the floor lies some 100 metres below. The temperature stays at about 11 °C all year.

Finds from the exit gallery show that people used the cave long before it was explored: flint arrowheads and human remains from the late Neolithic, a Bronze Age dagger and pottery, Roman coins of the first century AD. Systematic exploration began in 1840 with Antonio Federico Lindner, who was searching the Karst for underground water to supply the growing city of Trieste. The cave was mapped in 1897 and opened to the public by the Club Touristi Triestini in 1908. It is also a working laboratory: two horizontal pendulums hanging from about 100 metres, the longest geodetic pendulums in the world, are used by the University of Trieste to record tides of the Earth's crust, tectonic movement and distant earthquakes. A speleological museum stands beside the entrance.

Getting there

The cave lies at Borgo Grotta Gigante in the municipality of Sgonico, on the Karst plateau about 6.7 km from Trieste. The nearest airport is Trieste Airport (TRS), about 27 km away.