You can start your hike at the large parking lot and information desk of the Risnjak National Park, while the trail to the source begins a bit further, right by the Gorski Kotar House of Knowledge visitor centre. At first the trail descends gently, and then steeply, crossing the Krašićevica canyon before leading you to the source of Kupa, a turquoise lake which is sure to mesmerise you. The area has been protected since 1963, and it is one of Croatia’s strongest and deepest sources, sometimes called the “unsolved mystery of the karst” due to its unknown final depth.