Search: Sport Relief cycle challenge
Celebrity cyclists including Fearne Cotton and David Walliams will set off on a thousand mile ride from John O'Groats to Land's End aiming to raise £1 million for Sport Relief.
The first 24-hours of the non-stop relay ride will see the fundraisers tackle an overall hill ascent of almost 29,000ft - the equivalent of Mount Everest.
Television and presenter Cotton said: "When I was told that we would be climbing the equivalent of Mount Everest on the first day alone I thought it was a joke.
"But when you look at the route it's true - there's almost 29,000ft for us to pedal up on the Scottish leg of the trip. And a lot of that is in the dark!"
Little Britain star Walliams, who swam the English Channel for Sport Relief four years ago, said: "Water is one thing, but I'm not built for a bike. I'm not sure what I've let myself in for!"
They will be joined in the BT Sport Relief Million Pound Bike Ride by presenter Davina McCall and comedians Miranda Hart, Russell Howard and Patrick Kielty.
A seventh cyclist, comedian Jimmy Carr, will join the team along the way.
