Gacka River Springs — Majerovo Vrelo

The Gacka is one of Europe's most extraordinary karst rivers — a full-sized flow of crystal-clear water that emerges fully formed from three main springs on the floor of the Sinac plain and runs just 60 km before disappearing back underground at Švica. The largest of these, Majerovo Vrelo, is a jaw-dropping deep blue pool where 15 cubic metres of water per second boil silently out of a 40-metre-deep vertical cave shaft. A wooden footbridge crosses the spring right at the emergence point and old restored water mills line the immediate downstream bank; several have been converted into ethnographic exhibits or delightful trout restaurants. The Gacka is also one of the world's most famous fly-fishing rivers — its uniquely mineral-rich water grows brown trout to 5 kg and above, and permits are strictly limited to preserve the fishery. The nearby Tonković Vrelo (a five-minute walk downstream) and Pećina Vrelo are smaller but equally beautiful, with the third feeding a stone mill that still grinds Lika buckwheat to order for local ćiripaj bread. Bring a swimsuit — the pools are a very cold 8 °C year-round but locals still dive in.