In March 2012 four teams of celebrated sports people and celebrities will run, row, cycle and sail their way clockwise around the UK and Ireland representing England, Ireland, Scotland and Wales to raise money for Sport Relief.
Big Splash caught up with them as they took to the sea for a training exercise.
The teams will start simultaneously in their home cities of Cardiff, Dublin, Edinburgh and London as they run, row, cycle and sail their way clockwise around the UK and Ireland from 10-17 March.
For eight days they will push their bodies to the extreme as they raise a stack of money for Sport Relief. Every turn of the pedal, every stroke of the oar, will carry the hopes of a nation.
You can register to get involved and run the final six miles alongside the sports stars and celebrities by going to the First Nation Home website.
Visit the Sport Relief site for more information about how you can take in other fundraising events in 2012.
For more information on how you can get involved with swimming, visit the Big Splash website.