What gives a man the idea of setting up the world’s first international zipline ride – a business with all the bureaucracy inevitably associated with sliding people over a border at high speed?

“Two villages in two countries, separated by a river 150 metres wide – a zipline just seemed obvious to me,” says David Jarman, the British creator of Límite Zero, a new zipwire ride connecting the Spanish village of Sanlúcar de Guadiana with Alcoutim, across the Guardiana River in Portugal.

Though the two villages might be less than a minute apart if one is travelling down a wire on a pulley, a not-totally forgotten history of border disputes made the project difficult from the start. Jarman has spent the past four years battling red tape and establishing the operation, which this weekend will finally open for its first full season.

From the Chiringuito café in Sanlúcar I had seen the distant cable high above the river – a gossamer thread in the sun, hard to spot otherwise – and I had watched the occasional tiny figure, bent into an L-shape, flying across the sky. Standing on the zipwire platform as a “test zipper”, throwing myself into open space suddenly felt a lot less abstract. Three-quarters of a kilometre of heavy cable fell in a graceful parabola from just under Sanlúcar’s 17th-century hilltop fort. At some point the receding wire dwindled from sight, seeming to disappear mid-air high above the river.

The two villages seem to revel in their differences. Sanlúcar is stark and angular, with dazzling white buildings, and centres its social life on shouty, clattery bars. Alcoutim is washed in pastel shades and its tree-shaded café terraces have muted voices and better coffee. Small ferries cross between the villages but few locals use them. To further underline the contrast, Portugal’s clocks are an hour behind those in Spain.

Many older villagers remain mystified by the concept of people prepared to pay to do something as pointless as sliding down a wire to a country they wouldn’t want to visit. Some assumed that, given Iberia’s economic austerity, the zipline had been installed as a low-cost substitute for the bridge that was promised by politicians in the boom years. Younger residents are more positive. Five already have jobs with Límite Zero while others hope that thrill-seeking tourists from the Algarve and Costa de Luz will put the remote villages on the map and support spin-off businesses, whether restaurants, kayak trips, mountain bike trips or rural walks.

The word “test” in any experience involving gravity, height and speed inevitably sparks questions. As I adjusted my helmet and tightened the straps of a climbing harness around my legs and waist, I asked them. The Swiss-made galvanised steel cable is, apparently, based on ski-lift technology and has a 27-tonne breaking strain.

The expert in global ziplines who oversaw the project had been first down the line. Jarman was second. When it comes to entrepreneurs, I like them to demonstrate confidence in their own product.

“Right, both hands on the bars and keep your legs together and pointing forwards once you’re sliding,” said an instructor. I lifted my feet off the platform and started sliding. The harness took my weight. The pulley above began to whirr fast. And then much faster. I was swooping down the hillside as if contour flying. Scrub and bushes blurred beneath my feet.

Suddenly, it seemed, I soared off into the sky. The land had dropped away from under the cable and I was high above the river with nothing to relate my speed or movement to. It felt as though I was hanging motionless in the air, like a hovering kestrel. I had time to note the white blocks of the Sanlúcar houses off to one side like a spillage of sugar lumps. And to look down on the moored boats in the currents of brown water far below.

The stillness was an illusion. I was actually entering Portuguese airspace at about 80km an hour, having dropped almost 90m in a few seconds. Looking ahead, I saw orange trees. Goats were grazing around the landing platform. I flew over their heads. There was a violent deceleration as the pulley hit the brake and a nexus of elastic ropes and counterweights dragged and bounced me to a halt. I’d arrived. According to the Portuguese clocks, I had left Spain just under an hour before. An adrenalin hit, incredible views and a time-travel in one experience. As well as the promise of a nice cup of coffee.

Jasper Winn was a guest of Límite Zero (limitezero.com). The ride costs €15 per descent inclusive of ferry return from Portugal. Sanlúcar de Guadiana is 130km west of Seville. Alcoutim is 35km from the Algarve coast, 70km from Faro airport