Soča

Where it sits. The Soča rises at about 1,100 metres in the Trenta valley, on the southern side of the Julian Alps below Jalovec and Travnik, where it emerges from a karst cave mouth as a full-sized stream rather than a trickle. It runs 138 kilometres to the Adriatic near Monfalcone, 96 of them in Slovenia and the remainder in Italy, where it is called the Isonzo. The upper river passes Bovec, Kobarid and Tolmin, cutting through limestone in a succession of gorges before opening into the broad gravel plain below Nova Gorica. Its colour is the thing people remember: a saturated emerald green, produced by fine carbonate rock flour held in suspension and by the pale limestone bed reflecting light back through the water. Very few rivers in Europe hold that colour along their whole length, and the Soča does it in low water and high.

A river that was a front line. Between June 1915 and November 1917 the valley was the setting for twelve battles between Italy and Austria-Hungary, fought along the ridges and in the riverbed itself, with a combined toll of several hundred thousand dead and wounded. The twelfth battle, the breakthrough at Kobarid on 24 October 1917 that Italians call Caporetto, collapsed the Italian line and pushed the front back to the Piave. Ernest Hemingway, who served as an ambulance driver in Italy and was wounded on the Piave in 1918, made that retreat the spine of A Farewell to Arms. The evidence is still on the ground and unusually well curated: the Kobarid Museum, opened in 1990 and awarded the Council of Europe Museum Prize in 1993, is among the best First World War museums anywhere; the Italian charnel house above the town holds more than 7,000 named dead; and the Walk of Peace, a marked route of some 230 kilometres, links restored trenches, chapels, cemeteries and open-air positions from the Alps to the Adriatic.

On screen. The Soča is the most filmed landscape in Slovenia and its biggest international credit is The Chronicles of Narnia: Prince Caspian (2008, Andrew Adamson). The production's Slovenian unit worked the river around Bovec and Kobarid in the summer of 2007, using the green water and the pale limestone banks for the river sequences of the film's Narnia, ground that neither New Zealand nor the Czech studios could supply. Slovenian and Italian productions have used the valley for war drama for decades, drawn by the intact wartime infrastructure, and the river's rapids appear regularly in kayaking and adventure-sport films, since the Bovec section is one of the standard European whitewater venues. What draws all of them is the same quality: the valley reads on camera as wilderness while being served by an asphalt road for its entire length.

What you actually see today. From the source, reached by a steep secured path from the Trenta road, the river runs through the village of Soča and into the Velika korita, the Great Gorge — 750 metres of channel cut up to 15 metres deep and in places barely two metres wide, crossed by footbridges. Below Bovec the water opens out into the rafting section, graded III to IV in spring; above the town the Boka waterfall drops 106 metres out of a cliff face, the highest fall in Slovenia and at its most violent during snowmelt. At Kobarid the Napoleon Bridge spans a second narrow gorge, with the Kozjak waterfall — a 15-metre fall in a closed limestone chamber — a twenty-minute walk away. The river holds the marble trout, Salmo marmoratus, an endemic species nearly lost to hybridisation and now the subject of a long-running restocking programme; fishing is by permit and largely catch-and-release.

Getting there and timing. The valley is reached from Ljubljana in about two hours via Idrija and Tolmin, or in summer over the Vršič Pass from Kranjska Gora, a road of fifty numbered hairpins that is one of the finest drives in the Alps and closed by snow from roughly November to May. The Bohinj railway serves Most na Soči, with a car-shuttle train through the tunnel from Bohinjska Bistrica. May and June bring the coldest, fastest, greenest water and the best rafting; July and August warm the pools enough for swimming, though the river never becomes comfortable; late September empties the valley while the huts on the Krn ridge are still open.