Grotta Gigante

The Grotta Gigante is essentially one room: about ninety-eight metres high, seventy-six wide and one hundred and sixty-eight long by a 2011 laser survey, which for decades held records as the largest single cave chamber open to tourists, and it is still among the largest anywhere. Around five hundred steps descend into it and climb back out. Two geodetic pendulums hang from the roof on wires nearly a hundred metres long, installed to measure tiny deformations of the earth's crust and still recording, including the effects of distant earthquakes. The plateau above is classic karst, and the word karst itself comes from this region's name.

What you actually see

• The single chamber - a room nearly a hundred metres high underground.
• The geodetic pendulums - instruments measuring crustal movement.
• The 500 steps - the descent and climb back to the surface.
• The karst plateau - the landscape that gave karst its name.

When to go

Year-round; the cave holds about eleven degrees, so a jacket is needed in summer. Tours run at set times, hourly in season and less often in winter.

Honest expectations

Around five hundred steps each way, with no lift, which rules it out for limited mobility. Entry is on a fixed guided tour. It is cool and damp inside.

Nearby

Trieste lies below; the Slovenian border is close.