Vrelo Bune, Natural spring and heritage site in Blagaj, Bosnia and Herzegovina.

Vrelo Bune is a natural karst spring where water emerges from beneath a towering limestone cliff face. The water flows immediately into the Buna River, which continues downstream through the region.

The Buna rises from a karst cavern beneath a 200 m cliff, feeding a river that powered mills and fulling works. The Sufi tekke complex, with its guest house and türbe, likely arose shortly after Ottoman rule began in Herzegovina, around 1520 at the latest; the guest house predates 1664 and was rebuilt in 1851. The Karađoz-beg bridge, funded by Zaim hajji Mehmed-beg, predates 1570.

The name Vrelo Bune means "Buna Wellspring" in Serbo-Croatian. The Sufi lodge beside the spring, the Blagaj tekija, was likely founded around 1520, soon after Ottoman rule reached Herzegovina; its guest house (musafirhana) predates 1664 and was rebuilt in 1851. The lodge, its türbe mausoleum, the spring and the mills form one ensemble.

The spring pool sits at the foot of a 200 m cliff, with the tekke on the right bank and the mills and Velagić complex on the opposite side; a 2 m horseshoe-shaped weir closes the pool before the Buna narrows into a channel about 10 m wide. The water stays 7 to 8 °C, so the cave mouth feels cold even in summer.

The water emerging from the depths maintains the same cold temperature throughout the year. This consistency is unusual among large natural springs across Europe.