Less than 50 km apart in Northeast Italy and Slovenia are two impressively large cave systems, one noted for its massive main cavern and the other for its 24 km of cave tunnels. Grotta Gigante near Triste, Italy and the Postojna Cave in Postojna, Slovenia, are both karst caves formed as rainwater seeped into the limestone bedrock, causing erosion and forming caverns and tunnels. Both of these cave systems beautiful speleothem formations like columns, drapery, stalactites and stalagmites.
Grotta Gigante near Trieste
Trieste is an important port city along the northern Adriatic Sea, almost entirely surrounded by the Slovenian border. It was the fourth largest city in the Austro-Hungarian empire, and remains an important maritime gateway for Central Europe.
Located just outside Trieste, Grotta Gigante (meaning Giant Cave) features a massive central cavern that is 107 m (351 ft) high, 65 m (213 ft) wide and 130 m (430 ft) long. It was the world’s largest cave accessible to tourists until surpassed by a cave in France.
The cave was first explored in 1840 and opened to tourists in 1908.
Guided walks through the cave last approximately an hour. It’s 500 steps down, and 500 steps up.
If you’re up for more adventure, you can book the special “Speleo Adventure” where you’ll don a harness and helmet, and climb down a hidden branch of the cave to the level of groundwater. This area was first explored in 2005 and takes 4 hours.
Postojna Cave in Postojna, Slovenia
The Postojna Cave is the longest cave system in Europe accessible to the public, with over 24 km (15 miles) of tunnels. It has been a tourist destination since 1819, although there’s evidence of human use dating to 1213.
While the cave system is 24 km long, only 5 km is open to the public. The cave tour takes 1.5 hours, with visitors taking a train through 3.5 km of cave, and navigating another 1.5 km on foot.
The cave houses the world’s only underground post office, opened in 1899 so that tourists could mail a postcard with a cave postmark. It’s still in operation!
Planning your visits
Planning your visit to Grotta Gigante
Like almost all caves, the temperature is cool (11ºC) and humid all year round. A jacket and comfortable shoes are recommended.
Free parking is available, although Grotta Gigante can also be accessed by public transit. From Trieste (Piazza Oberdan), bus 42 will get you there in approximately 35 minutes (check the schedules; this route can be sporadic). From Opicina, you can also take a bus or walk (about 3km).
Visit the Grotta Gigante official website for the latest visitor information.
Planning your visit to the Postojna Cave
The Postojna Cave can be reach by car from Trieste, Ljubljana and other cities in Slovenia and even Croatia. Paid parking is available, including facilities for RVs and electric vehicle charging stations.
It’s also accessible by public transit. Depending on your location, take a train into Postojna, then it’s a short 2 km (25 minute) walk to the cave park (or get a taxi).
There are also bus routes from various nearby cities that go directly to the cave park, including from Trieste, Ljubljana, Zagreb and Rijeka. However, most of these are seasonal or sporadic, and will take more time than taking the train and walking.
Visit the Postojna Cave official website for the latest visitor information.