Transvulcania Ultramarathon 74km Spain

Mountains, volcanos, beaches, forests, a tropical rainforest, tiny villages and breathtaking views; La Palma is the jewel in the Canaries' crown. Many consider it to be the most beautiful and idyllic Canary Island – unspoilt by tourism and ideal for rest, peace and quiet, it is a treasure for the walker, hiker or runner.

Although the island is relatively small, it is shaped like a question mark and each curve has many surprisingly different areas of natural beauty. The south of the island is dominated by the dramatic Cumbre Vieja – a central spine of steep volcanos that create a blackened wasteland in stark contrast to the wild and green vistas of the north. Linking the two sides is the Caldera, the largest water-erosion crater in the world. Its steep slopes inside and out create a natural central ridge.

These incredible rock formations create the perfect landscape for a mountain race. The Transvulcania Ultramarathon follows the famous GR131 route that takes runners from the sea in the south to the sea in the north. In its origins, this path connected the localities furthest away from each other.

The race route starts at the Fuencaliente lighthouse at sea level and follows the GR131 all the way to Tazacorte port, finishing with a sting in the tail as runners are tested with a final climb up to the town in Los Llanos de Aridane. It's a logical route with no ambiguity.

Anna Frost, from New Zealand, has made the race her own ever since winning in 2012. 'The start is chaos, people sprint and then suddenly you are in a one-metre-wide trail. Rocks are everywhere, it's a black sandpit and it's dark. Along with that you have supporters making noise; it really is bonkers. To get around people you have to go around the rocks. It's a volcano, after all, and the floor moves. After Los Canarios, around seven kilometres, I like to push on.'

From Los Canarios, dense pine forests offer a stark contrast to the opening kilometres. Under foot, the terrain now mixes black lava sand with pine needles and rocks, but running is easier than the climb and offers an opportunity to stretch the legs to full stride.

Climbing up, the trees eventually start to subside and you emerge in the 'Route of the Volcanos'. The southern ridge of the island is where most of the volcanos are lined up. Early sections of the course include two key volcanos, San Antonio and Teneguía, the latter last erupting in 1971. The first kilometres are tough going, and most certainly a struggle on race day with some 1,500-plus runners. The path is often narrow, with loose black sand or rocks. It is an incredible route, sometimes very runnable, at other times hard work due to the increasing steepness of the path and loose, deep lava sand.

The final sections of the volcano route offer good, fast running to El Pilar. Heading north for the crest of La Cumbre Nueva, a forest trail leads to El Reventón (1,350 metres). Initially this section provides some of the easiest running so far; the gradients are easier and underfoot one has fewer obstacles.

The path climbs the successive and increasingly high peaks to the Taburiente crater. The rim is an incredible natural wonder, offering technical running terrain, constant changes in elevation and some of the most amazing views you will ever see. Depending on the weather systems, you will either have clear blue skies and the ability to look out into the distance for miles, or a thick, blanket-like layer of cloud that sits below your feet, making you feel as if you are literally skyrunning.

'I can't quite describe how beautiful the route was,' says competitor Marina Ranger. 'It really made up for, and sometimes even numbed, all of the pain I was feeling. Running above the clouds and around the crater of an extinct volcano was completely mesmerizing and the memories of it will stay will me forever. I thought that reaching the top meant I had conquered the race, but I hadn't quite realized how tough the last 22 kilometres was going to be. As you descend, the land becomes less barren and you begin to enter the pine forests again. There were some short runnable sections here, though they didn't last long as the technical ground was sure to slow you down at some point.'

La Palma is also distinctive for its microclimate, adding an extra element to the race's difficulty and, strangely, its appeal. Running the race will almost certainly put you through different types of weather, particularly if the cloud layer appears. You can be hot with the sun beating down on you, and then a little chilly as you run through the cloud.

From the Roque de los Muchachos (2,421 metres), the highest point of the course, the route drops down to the sea at the port of Tazacorte. Beware! Runners often think that they have a wonderful, long descent to the finish. They do, but it is steep, technical and punishes the legs. Easy running sections are followed by tough, technical, rocky and gnarly terrain.

Crossing a main road at El Time, a couple of very steep road sections follow before the final drop down the stunning (and technical) zigzag path to Tazacorte port. Frost picks up her story from 2014, when she set the course record: 'When you come down the zigzags you can hear the crowds in the port ... it is uplifting. I also had guys I was overtaking shouting encouragement, "Go Anna, go Anna." It was brilliant.'

The GR131 stops in Tazacorte, but the Transvulcania Ultramarathon organizers have a sting in the tail, as the final kilometres take you back up to the town of Los Llanos where a rapturous welcome awaits.

'Your legs are like jelly after running downhill for 90 minutes,' said Frost, telling the story of the closing kilometres. 'In the port I just refocused. The riverbed wasn't a surprise but when you hit the beach and your feet sink, it isn't great, particularly knowing the road is just at the side. Mentally it is exhausting, but it is a beautiful trail. You have cliff walls and you do get some shade. For me, I just knew it was nothing in the bigger picture, I knew I could hold on and keep going at a decent pace.'

The final roads of Los Llanos drag on as the heat beats down, but the crowds can be heard and they pull the runners in to a glorious finish. 'It's amazing; you can hear the noise from a long way off,' says Frost. 'The final stretch seems miles away. I...