Touring the huge, spectacular subterranean chambers of the 6km-long Škocjan Caves is a must. This remarkable cave system was carved out by the Reka River, which enters a gorge below the village of Škocjan and eventually flows into the Dead Lake, a sump at the end of the cave where it disappears. It surfaces again as the Timavo River at Duino in Italy, 34km northwest, before emptying into the Gulf of Trieste. Dress warmly and wear good walking shoes.
There are two options for touring the caves. The first is a two-hour guided tour through the caves (the most popular option for visitors, called Through the Underground Canyon). Visitors walk in groups from the ticket office for about 600m down a gravel path to the main entrance in the Globočak Valley. Through a 116m-long tunnel built in 1933, you soon reach the head of the so-called Silent Cave, a dry branch of the underground canyon that stretches for 500m. The first section, called Paradise, is filled with beautiful stalactites, stalagmites and flowstones that look like snowdrifts; the second part (called Calvary) was once the riverbed. The Silent Cave ends at the Great Hall, 120m wide and 30m high. It is a jungle of exotic dripstones and deposits; keep an eye out for the mighty stalagmites called the Giants and the Pipe Organ.
The sound of the Reka River heralds your entry into the Murmuring Cave, with walls 100m high. To get over the Reka and into Müller Hall, you must cross Cerkevnik Bridge, suspended nearly 50m above the riverbed and surely the highlight of the trip.
Schmidl Hall, the final section, emerges into the Velika Dolina (Big Valley). From here you walk past Tominč Cave, where finds from a prehistoric settlement have been unearthed, and over a walkway near the Natural Bridge. The tour ends at a funicular lift that takes you back to the entrance (or you can opt to walk, which takes about 30 minutes).
The Škocjan Caves are home to a surprising amount of flora and fauna; your guide will point out mounds of bat guano. The temperature is constant at 12°C so bring along a jacket or sweater. Also note the paths are sometimes slippery. In total, visitors walk 3km on this tour. There's a 'no photos' rule.
From April to October, visitors can choose a second tour option, called Following the Reka River Underground. This is a guided (or self-guided) 2km walk following the path of the Reka River, entering the first part of the cave through the natural entrance carved by the river below the village of Škocjan. Tickets for this option cost adult/child €11/5.50; a combined ticket with Through the Underground Canyon costs €21/11.