Mystery of the black cave

Vrelo Bune (Serbian Cyrillic: Врело Буне) is the natural and architectural ensemble at the Buna river spring near Blagaj kasaba, southeast of Mostar (Bosnia and Herzegovina, BiH). Buna is a very short river and after mere 9 km it makes a left bank tributary of Neretva. The source of the Buna river is the finest example of an underground karst river, where a strong spring emergescfrom a huge cavern beneath a high vertical cliff. This is one of the largest and most beautiful springs in Europe, producing approx. 30 m3/s with extremely cold, pristine water.