The story begins with money and rock. Late in the nineteenth century, rights to the rich iron deposits at Ojos Negros were granted to a group of Basque businessmen, who founded the Compañía Minera de Sierra Menera in 1900. The quality of the ore was excellent and the quantity vast, but the existing Teruel–Sagunto railway would not carry it on acceptable terms. So the company simply built its own line - a narrow-gauge railway running all the way to the Mediterranean coast, engineered to bear the relentless weight of loaded ore wagons. For seven decades it did exactly that, until changing economics finally shut it down and the Sierra Menera company collapsed.

In 2001 the Valencian regional government began converting its share of the abandoned line into a rail trail, and Aragon soon did the same for the stretch within its borders. The result is the Vía Verde de Ojos Negros, at 160 kilometres the longest greenway in Spain and part of a national 'Vía Verde' network of some 2,700 kilometres built on disused railways. Plans have long been discussed to extend it right into the city of Valencia. What was once a private industrial artery, closed to everyone but the mining company, is now open to anyone with a bicycle, a pair of boots, or a horse.

Because it was engineered for heavily laden trains, the trail climbs with the patience of a railway, never steeper than a gentle 3 to 5 percent. It divides into two great stages. The first, Ojos Negros I, runs about 70 kilometres inland from Algimia d'Alfara in Valencia up to Barracas, rising some 800 metres from the Mediterranean plain to the edge of the central plateau through 15 old railway tunnels and across eight bridges. The second, Ojos Negros II, continues 91 kilometres from Barracas to Santa Eulalia del Campo in Teruel, crossing 13 viaducts and topping out at the Escandón Pass, 1,218 metres above sea level. Along the way it passes Sarrión, known as the truffle capital of the world.

A rail grade makes a superb sightseeing route, because railways were laid to link places worth reaching. The Ojos Negros greenway threads together a string of them: Segorbe, with its cathedral and medieval walls; Jérica, crowned by a Mudéjar bell tower declared a national monument; and the extraordinary provincial city of Teruel, itself famous for Mudéjar architecture. The corridor also brushes past dozens of protected natural areas, among them the wooded ridges of the Sierra Calderona and the Sierra del Espadán, so a single day's ride can carry you from cathedral squares to pine and oak forest without ever facing a serious hill.

The gentle railway gradient makes the whole route accessible - to families, to older riders, and to people with disabilities, who can travel long stretches that a normal mountain trail would put out of reach. Weather is the main thing to plan around. The Valencian coast is hot and dry in summer, while up on the Teruel plateau winters bring sub-zero cold and snow, so spring and autumn are the ideal seasons to travel the full length. To ride it end to end is to retrace, in reverse, the journey the ore once made - climbing from the warm Mediterranean up through tunnels and viaducts to the high, cold country where the iron was dug, on a road that industry built and left behind for everyone else.