The source of the Kupa river is nothing short of a hydrological and landscape phenomenon, and its beauty and wild nature leave a strong, lasting impression on every visitor. The source is located within the boundaries of the Risnjak National Park, nestled 100 metres below tall, vertical rocks. It is around 200 metres long and 50 metres wide, and has the appearance of a small, oval lake. The surface water is calm, clear and greenish in colour, sitting at an altitude of 321 metres above sea level.

The Kupa river emerges from a still unknown depth. However, the water was found to spring out of two separate channels resembling vertical wells. Although a depth of over 80 metreswas measured in the deeper and narrower channel, while the wider channel was found to be 57 metres deep, the total depth of the Kupa river source remains unknown due to the low and constant water temperature ranging from 5 to 6 °C, making it impossible to dive into the deep waters. However, water colouring found an underwater connection between the Malenca sinkhole, as well as the Velika Voda stream sinkhole by Crni Lug, and the Kupa river. The water outflow capacity is approximately 1200 l/s,while maximum water quantities cannot be measured.

The easiest way to the Kupa river source is down a marked hiking trail from the village of Razloge, where you will find the information desk of the Risnjak National Park. The pleasant stroll through the beach forest takes approximately 30 minutes, and requires a bit more caution in the steep sections, to avoid slipping on wet leaves. The administration of the National Park set up a wooden fence and constructed a walkway in the more exposed parts. In the lower area, right by the source, the trail takes you through the dry river bed of the Krašićevica stream, which becomes impassable in heavy precipitation as the stream gets flooded.

The source can also be accessed from the opposite side of the Kupa river, from the direction of Kupari or from the village of Hrvatsko, where Čabranka flows into Kupa. This trail is a bit longer (5 kilometres), but not demanding thanks to its configuration.