On the right side of the last viewing platform onto Strbački Buk waterfall, you find this very hidden sign, showing towards a little path into the forest. You can hike 3 kilometers to Crno Vrelo and back. I did not do this hike myself (yet) because we unfortunately didn't have time. But I am very sure, it can only be worth it, so I wanted to include it in this list – especially because you cannot find anything about it online or even on the National Parks website.