The cave of the spring of the Mokranjska Miljacka is located not far from Kadino selo (near Mokro – the hamlet of Vrelo) at the foot of the limestone massif of Gradina and is the longest cave in the Republic of Srpska. Animal species completely new to science were found in the cave. As its name suggests, the cave is located at the very source of the Mokranjska Miljacka. The temperature of the water at the spring is always around 6.2 degrees Celsius, thus it is necessary to use special equipment to visit the cave. Due to its natural characteristics, it provides excellent opportunities for extreme and adventure tourism. It is located at about 1,100 m above sea level, and the entrance to the cave is 4 m wide and 5 m high.
The entrance to the cave is made more difficult by water, especially on days when there is a lot of precipitation (then the water depth at the entrance is up to 50 cm). When there is no precipitation, the height of the water is about 20 cm, and the cave can be easily entered up to some 30 meters. After that you come to the first smaller lake which can be crossed on the left side over the sloping part of the cave wall where the water is shallowest. The second lake is separated from the first by only one embankment. It is about 1.5 m deep, and the use of a boat is recommended to cross this lake. After this there is a third lake which is connected to the other by a small culvert, so it is necessary to transfer the boat over the embankment.
The third lake is the largest – it is about 11.5 m long, with a depth of more than 2 m and a width of 2 m. The third lake does not actually end after these 11.5 meters but continues to the left, where you enter the fossil part of the cave which begins with an impressive hall about 20 m wide which is very rich in cave jewelry (stalactites, stalagmites, tubes, pizolites and more). The complete floor of the fossil part of the cave is covered with tubs that are mostly filled with water. This is a description of the first part of the cave (about 1000 m from the entrance). Further research reached up to 6800 m in depth, which means that this cave is huge and certainly the largest in the Republic of Srpska. A good part of the side channels of the cave still remain unexplored due to its inaccessible position.