These spectacular pictures show intrepid sportsmen indulging in the latest extreme trend - mountain unicycling.
While the one-wheeled cycles may more usually be associated with the circus, there is nothing jokey about the sport.
It takes nerves of steel to throw yourself down a rocky slope on the unbalanced vehicle, and nasty scrapes are common for the adrenaline junkies.
Brave: Adrenaline junkies throwing themselves down the Cornish hills on unicycles as part of a new trend
Epic scale: The unicyclists pause on a crag to take in the spectacular scenery of St Austell
Kevin Callaby has joined with fellow enthusiasts in St Austell, Cornwall to form the Mountain Unicycling Club Kernow - known as 'MUCK'.
They must pivot and 'bunny hop' from rock to rock as they descend mountains, hillsides and treacherous coastal paths on their custom-made bikes.
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The cycles are given mountain bike tyres to help them cope with the unforgiving terrain.
Mountain unicycling, also known as 'muni', has been popular in the U.S. for two decades but has only just caught on in Britain.
Landscape: A unicyclist from Mountain Unicycling Club Kernow admires the threatening rocks he has cycled down
Trend: The extreme sport started in the U.S. but has now arrived in the UK with the formation of MUCK
Day out: The club has around 20 members who enjoy the challenge of unicycling on mountains
Mr Callaby, whose club is the first in the country, said: 'One of the earliest exponents described mountain unicycling as a cross between mountain biking and rodeo riding, and I think that's absolutely spot on.
'You can expect a few bumps and scrapes but there's actually very little chance of injury because, unlike a bike, a set of skis or a snowboard, you're not tangled up in anything.
'You can simply bail out and use your hands and feet to cushion your fall.'
One of the most common injuries suffered by practitioners are gashed and bruised shins - known as 'shindentations'.
Off he goes! Another daredevil throws himself down the hill, risking a number of serious injuries
Unusual: Unicycles are more often associated with jugglers and circuses than outdoor pursuits
Otherwordly: The strange terrain of parts of Cornwall is perfect for lovers of extreme sports
Mr Callaby, a 34-year-old solar panel fitter who used to perform with the Moscow State Circus, is no stranger to unicycles - he has been riding them since the age of just nine.
'Until about five years ago I used to just ride down the road, but then unicycles got better which meant you could go off-road,' he said.
'We started off with coastal bike paths but then we began to search for more difficult terrain. We look to ride down stuff that is really steep and really loose.
'You always have a minimal point of contract with the ground, so it's about balance, skill and coping with what the terrain throws at you.
'It doesn't have to be a mountain, you can unicycle down a set of stairs or even just a slippery kerb - anything that presents a challenge.'