The Vrelo cave in Fužine was discovered by accident in the 1950s, during the construction of the Bajer lake. It is estimated to be 3.5–4 million years old. Although it only measures 300 metres in length, it is exceptionally beautiful and rich in cave decorations. Its beauty is further complemented by a stunning mountain spring, a lake and a sinkhole, at a depth of only about fifty metres. The clear, cold mountain stream flowing from the Ličanka river basin floods the cave in times of heavy rainfall. Interestingly, the Vrelo cave measures 8 °C in air temperature year-round.

Owing to its beauty, the cave is often nicknamed “Little Postojna” after the renowned Postojna Cave. Vrelo is adapted for visitors, and in 1998, it underwent renovations to set up new lighting fixtures and a hiking trail with small bridges. Due to its smooth terrain configuration with no step-ups, it is the only adapted cave in Europe suitable for all ages, from children to elders, as well as wheelchair users.

The Vrelo cave is visited by more than 10,000 people every year.