Almost on the border with Croatia, the UNESCO-listed Vjetrenica cave system is the deepest in Bosnia and Herzegovina, disappearing 3.7 miles (six km) below the Dinaric Alps into a magical world of subterranean rivers, limestone galleries and glittering lakes. Spectacular tumbling stalagmites and stalactites loom in the semi-darkness of the meandering tunnels and its ever-running waters flow into the Trebisnjica River on the southern edge of the Popovo Polje valley.
Skeletons of bears and leopards have been found in the Vjetrenica caves along with primitive drawings dating back 10,000 years, which can clearly be seen etched into the walls. Many hundreds of rare animal species have been discovered here, including the olm, a salamander-cum-fish with legs, lungs and gills that is peculiar to the region. Visited by thousands before the tragic civil war of the 1990s tore former Yugoslavia apart, infrastructure for tourism at Vjetrenica has recently been upgraded and the caves are once more open to explore. Temperatures underground are at a constant and cool 11°C, so dress warmly as guided tours last around 60 minutes. As the underground pathways are slippery, take sturdy footwear; jackets and hard hats are provided.
Zavala. Opening hours: Apr–May Mon–Sat 10am–2pm; Sun 12pm–2pm. June–Oct Mon–Sat 10am–6pm; Sun 12pm–6pm. Outside these months, visits can be arranged on request. Admission: adults 10 KM; seniors & students 8 KM; children 4–15 5 KM. If coming to Vjetrenica from the Croatian side of the border, a passport is required.