In terms of hydrographical and aesthetic characteristics, the most important and valuable part of Gorski kotar is the Kupa valley. In addition to the attractive features of the Kupa valley at this point we would like to mention some other attractions for those interested in hiking, caving, etc.
Tucked away on the upper slopes of Drgomalj hill is the most beautiful and largest cave in Gorski kotar, Hajdova hiža. Together with the nearby vista point offering a breathtaking view to the north and the entire Kupa valley below, it forms a natural phenomenon of unique beauty. The access to Hajdova hiža is difficult, so the cave is not suitable for tourist visits but remains a challenge for those seeking adventure and properly equipped.
The upper course of the Kupa is often described as the magnificent valley of butterflies. Mr. Mladen Kučinić, a biologist with the Croatian Natural History Museum, has an explanation for that: "Along some twenty kilometres of the upper Kupa, human settlements and activities blend discreetly with the intact landscapes to establish beautiful, undisturbed harmony, characteristic of this part of Croatia, which is often said to be one of its most beautiful corners. Such natural conditions support the specific flora and fauna found only in this part of Gorski kotar. The studies carried out to date have identified almost 500 different species, and the number is not final. It shows an extraordinary range of faunas, in particular daylight butterflies. In this small area alone, there are 108 species of butterflies, which makes up 60% of the total number of butterflies found in Croatia. Such abundance of the butterfly species is best illustrated by the fact that in the entire United Kingdom only 56 species of butterflies are found. Two new endemic butterfly sub-species have been identified here. This is a unique example in Croatia and can be ascribed to the geographical isolation of the upper Kupa area, which has provoked certain specific evolutionary processes resulting in the occurrence of these sub-species. Bearing all this in mind, it is important to preserve for future generations not only the Upper Kupa, but its entire course as an area of great bio-diversity and Croatia's unique example of a river valley."