Last year, Ben and Carl cycled from Marble Arch to the Arc de Triomphe in 24 hours. But this year, they decided to take it up a gear... 

On Thursday 27 July, they'll be setting off on a 400-mile cycle from Windsor Castle to Edinburgh Castle - which they aim to complete in just 48 hours. 

In total, the pair will climb more than 8,856 metres - 8 metres higher than Mount Everest. 

Surely a challenge worthy of sponsorship...

The pair will be raising money for Great Ormond Street Hospital. And any donation, large or small, will be greatly appreciated and will hopefully spur them on as they fight fatigue to reach the finish line before the clock runs out. 

You can follow their progress on Twitter at @TourdeEdinburgh2017 and #TourdeEdinburgh2017.

Here's the blurb from JustGiving which explains how they deal with your donation:

Donating through JustGiving is simple, fast and totally secure. Your details are safe with JustGiving - they'll never sell them on or send unwanted emails. Once you donate, they'll send your money directly to the charity. So it's the most efficient way to donate - saving time and cutting costs for the charity.