Vrelo Bune (Serbian Cyrillic: Врело Буне) is the natural and architectural ensemble at the Buna river spring near Blagaj kasaba (village-town) and a part of the wider "Townscape ensemble of the town of Blagaj — Historical and Natural Heritage of Bosnia and Herzegovina" (Ottoman Mediterranean architecture, 1520), southeast of Mostar, Bosnia and Herzegovina. It is impossible to separate the natural values from the cultural and historical heritage of Blagaj, since its distinctive quality is in the coexistence of the natural and the man-made, in the integration of the physical structure into the landscape.

The Buna river is a short river in Bosnia and Herzegovina and it is a left bank tributary of the Neretva river. Its source (Bosnian: Vrelo Bune) is a strong karstic spring, emerging from a huge karstic cavern beneath a high vertical cliff. This region is specific for the diversity of its above-ground and underground hydrography. The source of the Buna river is the finest example of an underground karst river. It's one of the largest and most beautiful springs in Europe, producing approx. 30 m³/s with extremely cold and clean water.