Extreme point-to-point triathlon City to Summit will see many more competitors taking on the challenge in Scotland this May, which involves a run to the very summit of Britain's highest mountain, Ben Nevis.
The race starts on 31 May with a 3.8km swim in the chilly Forth of Forth, then sends athletes on a 180km bike stage into the Scottish Highlands and on to the shores of Loch Leven. The final stage involves a 42km run up Ben Nevis and down to the finish line in Glen Nevis.
Last year's inaugural event saw 196 people take on the challenge, which promises cold temperatures and snow on the mountain's summit again this year. Entries to the 2014 event are open now and cost £275 per person for Solo Entry into the 1-day “Expert” class.
UK's toughest triathlons
Like the idea of a tough triathlon? Here are some other UK-based options:
Ironman Wales: With a punishing course across the Pembrokeshire countryside that involves a constantly changing gradient, this is seen as one of the hardest IM races going.
Helvellyn Triathlon: With a finishing line described by the Guardian as "like a depiction of hell", this monstrously difficult race takes in some of the country's most beautiful scenery.
Jurassic Man Extreme: As with the City to Summit race, this is a point-to-point triathlon that "makes grown men cry", according to the organisers.
The Brutal: With half, full and double-Iron distances on offer, and all requiring a run up Mount Snowden, this is viewed by many as the country's hardest race.
Celtman: Another tricky point-to-point one, this is an Iron-distance race across some of Scotland's most challenging terrain.