Vjeternica (which means 'wind cave') is the largest cave in Bosnia and Herzegovina. In the warmer parts of the year a cold air blows from its entrance. The cave has been explored and described to a total of about 6.1 thousand meters in length; of this the main canal is about 2.47 thousand metres long (from the edge of Popovo polje to the south). There are several permanent and occasional streams, and lakes, which the largest is about 180 m long. There are many stalactites, flowstone, draperies, cascades and others forms. In terms of its biological diversity it is one of the richest caves in the world. It is officially in second place, with 85 troglobionates. The remains of eight fossilised animals have bee found in it, the largest being the cave bear (Carnivoria, Ursus spelacus) and one comlete skeleton of leopard (Carnivoria, Panthera pardus). On the rocks at the entrance to the cave there are two carved stones, typical for Medieval tombstones in the region. In a scientific sense, Vjetrenica has been the site of many different forms of research, which may be traced back to the 16th century. Pliny the Elder in his work 'Historia naturalis' mentions a nameless cave from which a strong whirlwind blows, and he was actully referring to Vjeternica. Vjeternica has been visited by thousands of tourists until 1991, when in the fighting tourist equipement was destroyed.