After a leg-burning 45 minutes I finally reach the summit, 340m above the level of the Bristol Channel. I'm out of breath, knackered and I've got a thirst Oliver Reed would have been proud of. After a few glugs from my bottle (Vimto, not vodka) and a couple of bites on a muesli bar, I'm ready to take in the view.
With the sun approaching the horizon, the hills are bathed in a beautiful glow that's half sunset, half forest mist. I feel incredibly lucky. I'm riding a full-suspension mountain bike in one of the best trail centres in the UK. No matter which way I go from here, it's all downhill. I feel like I've earned the next bit of excitement, and set off with a little celebratory wheelie.
I'm 36-years-old. My location is Afan Forest Park in South Wales, one of a growing number of purpose-built mountain biking destinations in Britain. They offer a broad range of riding terrain, but all deliver stunning views.
The first was Coed y Brenin on the edge of the Snowdonia National Park: a hand-built track through its forest opened in 1999, and mountain bikers were lured with a visitor centre, café and bike shop. It was an environmentally aware, locally focused project long before such things were fashionable. Most of the centres it helped to spawn are in areas of outstanding natural beauty. After the success of Coed y Brenin, the Forestry Commission concluded that a similar trail in South Wales might attract some 200,000 cyclists to the region, generate an annual £18m and create 550 jobs.
Afan Forest Park's cycle trails were given the green light, and a select crew of expert trail-builders moved in; the results of which I was about to test. Flying through trees on a finely tuned mountain bike combines the thrills of downhill skiing, the grace of snowboarding and the child-like brilliance of skid-pulling. It's addictive stuff. For men of a certain age, there's a hint of Evel Knievel in the riding, and enough high-tech components and gadgetry to raise even James Bond's eyebrows.
There are obvious dangers of course – colliding with trees, large rocks or bobble-hatted ramblers to name just three – but the rewards are worth it. Where else can you get a full-body workout and that scream-at-the-moon rush lacking in daily life? Add in the fact that most runs feature a café stop (cake being the staple diet of most mountain bikers) and it's easy to see why the sport is often referred to as the fastest growing in Britain.
To meet demand, Afan's second visitor centre opened in 2005, and the £1m Glyncorrwg Mountain Bike Centre now houses the Skyline Bike Shop, Drop Off café, showers, and a bike wash area. With trails connecting it to the original visitor centre, riders depart safe in the knowledge that there's a snack waiting half-way through their run.
Along with the grub, diversity also helps. Like Alpine ski runs, Afan's trails are colour-coded. Purple runs are family-friendly roads rambling through the forest and take in strategic stops for picnics and views. Red runs are trickier and feature steeper, more technical descents, jumps. Black runs – as many skiers will recognise – are for experts only. Of the six trails on offer at Afan, one is purple-graded, four red and one black.
I chose the Penhydd trail, a 17km red trail starting at the visitor centre, that ascends Mynydd Penhydd and loops back to the starting point. In between, a series of tough climbs and thrilling descents keeps the heart rate in triple figures for the estimated course time of two to three hours.
The Penhydd path is easy to follow and its makers have gone to extraordinary lengths to tease every bit of energy from the available downhill, so that the track twists and turns down the steeper sections, and straightens out on the flatter parts. For a rider of my low-skill level it's perfect.
In places, the track narrows to near shoulder width, with a sheer drop on one side. The forest here has a magical, eerie quality, and the trail weaves through spectacularly remote sections. I slalomed past stumps, ducked under branches and steered around some devious boulders.
The trick is to read the terrain ahead, lean through the corners and only brake on a straight section. Mountain bike riders call this "flow", and it requires complete concentration. Exhilarated, I finished one downhill burst by plunging through a beautifully clear and surprisingly deep stream, parting it like a 30km/h Moses.
For those looking for even more excitement, nearby Cwmcarn has a permanent downhill track with death-defying jumps and terrain, and a shuttle service so you don't have to ride to the top.
Personally, I prefer Afan's approach. The riding is more like a very energetic ramble. The downhill rewards seem more worthwhile after having earned them with some tough uphill sections, and like all great mountain destinations, there is something about Afan that adds up to more than an inventory of its facilities. Perhaps it's the regeneration in this once-derelict ex-mining valley, now experiencing a tourism boom. Or maybe it's the ancient, welcoming forest. Either way, there's magic in them hills. Magic, and some spectacular cake.
Chris Moran is the author of Mountain Biking Britain, a guide to the best trail centres and riding spots in the UK, available now from footprintbooks.com
*Afan Forest Park is 8km north of junction 40 on the M4 and around 20km east of Cardiff. Cycle hire is available from either the Afan Forest Park or Glyncorrwg visitor centres from around £20 per day. The trails are free to ride and open 24 hours a day year-round.
Cwmdown bus: cwmdown.co.uk