Runners including Jamie Oliver, Jack Whitehall and Princess Beatrice will be pounding the pavements in a marathon from London through Kent.
Ten people are taking on the Virgin Strive Challenge - a 1,000km journey from London to the Matterhorn with marathons, rowing, cycling, hiking and climbing.
The first stage of the challenge began this morning as a team of runners, including Sam Branson, son of Sir Richard, set off from the 02.
They will be heading through Dartford and Gravesham before stopping in the town later today.
It will continue tomorrow leaving Gravesend and heading to Faversham and on Saturday will be going from Faversham, through Canterbury and on to Dover.
The event is raising money for Big Change, a charity founded by Sam and Princess Beatrice in 2010, created to support and offer guidance to youngsters.
The team also hopes Strive will inspire children across the country to develop better life skills, such as communication and self-confidence.
The challenge started this morning morning and will finish on September 5 in Switzerland.
The core team will run for 78.6 miles, row for 36 miles, cycle for over 900km, hike for 150km and climb nearly 2,000 vertical metres from Zermatt to the summit of the Matterhorn.
The runners finishing line was the Great Western hotel in Hever Court Road.
Once there the were informed someone had turned one of the signs around meaning runners had gone five miles out of their way.
One of those first over the line was Lara Milward who is a member of the 'core team' and runs her own fitness business.
She said: "It was very hard work but it was lovely to meet the participants, the people that are coming along and joining us at each stage.
"I haven't listened to any of my music because we were just chatting and finding out where people are from and what they're doing for the charity.
"Someone switched the signs around so we went five miles the wrong way so that was a bit naughty but the spirit has been wonderful."
Also greeting people at the finishing line was Eve Branson - Sir Richard's mum.
She added: "I always support Richard and now I'm supporting my grandson.
"Everyone here is doing mad things, which is typical of my family. They're not just raising money, they're earning it and they're thoroughly enjoying it.
"I think when they row across the Channel, that's going to be difficult - we've got a storm coming, so that's a bit worrying.
"I think more people should do this sort of thing. We've got to do more mad things in this world."
See today's route below.