In Risnjak National Park, there is the source of the Kupa River, one of the strongest, most widespread and deepest Croatian springs. At an altitude of 321 m above sea level, the water has formed a green-blue lake that will enchant you. The upper course of the Kupa River is called the Miraculous Valley of Butterflies due to the richness of its flora and fauna. A visit to the source of Kupa is possible from two directions within the borders of the national park - from the village of Razloge, 15 km from Crni Lug, and from the village of Kupari, 30 km away. Due to the narrow roads, the Razloge entrance is recommended.

The hiking trail from Razlog has a serpentine character, so it will take you about half an hour to walk to the source, while the return trip should take twice as long. You can also reach the source from the village Hrvatsko (Crni Lug – Hrvatsko 45 min drive) via Kupar. The path from Kupar is laid along the watercourse itself and will take you to the spring in about 30 minutes. To return, you can use the path that stretches along the right bank, parallel to the course of the river.