The area of Vrbas Adventure Resort has terrain for which karst forms such as sinkholes, caves, pits, sinkholes, springs, etc are characteristic. One of the karst sources is located in Krupa na Vrbasu which creates the Krupa river, for which is named. Sinking in Podrašničko polje near Mrkonjic Grad, a little river Ponor falls down into the depths of the earth’s crust, in order to see the daylight in underground systems again, but this time with a new identity poured into the Krupa river. The legend says that the Krupa River used to rise out of today’s Strikina pećina and that the sources fall down several dozen meters below because of the tectonic disturbances.
