The spectacular setting of the Himalayas is the battleground for the Yak Attack -- a 400km feat of mountain biking endurance and nerve. IInvolving 12,000m of climbing over the highest mountain pass in the world, competitors have to cope with the effects of altitude, frostbite and snow blindness.
Desert challenge —
The Four Deserts ultramarathon race series challenges competitors to take part in races in the Gobi Desert, the Sahara, the Atacama and Antartica. Each race covers 250km over seven days in some of the world's most inhospitable climates. Athletes carry their own food and equipment with only limited assistance.
Alpine wonders —
Paragliding experience and a heap of endurance are the requirements if you take part in the Red Bull X-Alps - a biennial event which requires competitors to traverse the length of the European Alps -- nearly 900km -- from Salzburg in Austria to the Principality of Monaco. The route goes from mountain top to mountain top but you must also trek with all your equipment.
In the footsteps of Scott —
The EWR South Pole Race tests competitors to the limit as they brave bitter temperatures of -40C and blinding snowstorms in their trek across the infamous Antarctic Polar Plateau in the footsteps of great explorers such as British Captain Robert Scott and the Norwegian Captain Roald Amundsen.
Hard core ultra distance —
An ultra distance race of 100 miles (160km) is tough enough but the Western States 100 has athletes battling high altitude in the Squaw Valley at 1900m and and over 5500m of climbing -- all in under 30 hours.
Triple test —
The Norseman in Norway is surely among the toughest of all ironman events with the start seeing athletes jump into a freezing fjord to swim 3.8km. They cycle 180km through mountainous terrain and the 42km marathon run finishes on top of the 1880m Gaustatoppen mountain.
Amazonian feats —
Competitors in Earth in the Jungle Marathon tackle 220km of inhospitable terrain in seven days, battling swamps, poisonous trees and intense heat in the Amazon. Athletes are self-supported to toughen the challenge.
Patagonian adventure —
Patagonia is a forbidding but spectacular setting for an endurance adventure race. The teams of four in the Patagonia Expendition Race must tackle 600km -- using foot, bike and kayak over multiple days in the territory straddling Argentina and Chile.
Race Across America —
The concept is simple. Cycle 4828km across the United States, either in teams or alone. No less than 51,800m of climbing are involved as you cross 12 states from California to Maryland. The cut off time is just 12 days which means sleep deprivation and exhaustion are major issues, not to mention the changing weather conditions.
Triathlon's blue riband event —
The Hawaii Ironman is the most famous event in triathlon but also among its toughest. Intense heat and crosswinds bring competitors to their knees as they tackle the 3.8km swim, 180km bike ride and marathon run on Kona Island.
Dead Sea test —
The Dead Sea ultra marathon is a 48.7km run with a difference as competitors go from a starting point over 900m above sea level in Amman to finish at the Dead Sea at 400m below sea level. Heat is a major inhibiting factor in this endurance test.
Chill factor —
The Swedish archipelago is the setting for the Otillo, which sees teams of two swim 10km and run 54km over the course of 14 hours. The cold water is continually entered and exited and many choose to swim in their shoes, even wearing a rucksack, and run in wetsuits.
Mountain bike epic —
The Cape Epic in South Africa is one of the most famous mountain bike races in the world with teams of two competing over 966km of terrain over six stages with massive climbs and daunting terrain.
Height of endurance —
Alpine climbing is the order of the day in the La Haute Route which starts in Geneva and finishes in Nice. Competitors can expect to ride around 730km over seven stages, with up to 17,000m of ascent. Many of the classic cols of the Tour de France are tackled on the way.
Comrades on foot —
The start of the annual Comrades Marathon -- a famous ultra distance running race -- which sees over 12,000 runners tackle the 89.2km from Durban to Pietermaritzburg in South Africa.