Italy: Grotto Gigante

Grotto Gigante is massive cave near Trieste famous for its enormous single chamber, the Grande Caverna, with the volume of about 365,000 cubic m. It held the Guinness World Record as the largest tourist cave in the world from 1995 until 2010, when La Verna cave in France was opened to tourists. The tour descends 500 steps to the bottom of the chamber and then ascends 500 steps up to the top. Along the way – lots of stalactites and stalagmites and other cave formations – including the 12m-high Colonna Ruggero, a stalagmite that has grown over 200,000 years at a rate of about 1mm every 15–20 years. The temperature inside is contact 11 Celsius. The cave also hosts two hanging Contino. Instruments – geodetic pendulums to measure Earth’s tides and crustal movements – longest such instruments in the world.