The Papuk underground – numerous caves, pits, and abysses – are habitat to interesting sorts of invertebrate, but they are also especially important as winter habitats and mating places for bats. They exist on the highest, karst area of the mountains Papuk and Krndija.
In the abyss Uviraljka, 11 sorts of bats were recorded during winter, what makes this sink a significant winter habitat for bats in European measures. Among the registered sorts, there is the endangered Bechstein´s bat (Myotis bechsteinii), and Uviraljka is the only known winter habitat of the Pond bat (Myotis dsycneme) in Croatia.
The abyss Uviraljka consists of more than 200 m mazes of narrow tunnels and is more than 30 m deep. The cave Kovačica is a unique abyss, more than 100 m long. The cave Suhodolka is the deepest cave in the continental part of Croatia, deeper than 90 meters. In the underground of Papuk, more than 80 animal species are recorded. Here live troglobiontic shrimps, of the gender Niphargus. That is a true underground species, without pigments on their body, or developed eyes.