Get discounted places
Sign up before 11 February 2018 and get a discount when you register for two places (either on two Ultra Challenge events or two people on one event). You could save £30 - so get in there quick!
A unique way to see the capital
This challenge sets out from Putney Bridge and heads East towards the City, zig-zagging over the incredible array of historic bridges that our capital has to offer - each with its own fascinating story.
There's a halfway rest in Vauxhall for some snacks and drinks.
And at the end of the 25km the brilliant finish line celebration is in Southwark, just past the world famous Tower Bridge.
With 2,000 participants its a popular and lively event and a unique way to explore the heritage of the capital.
To join up just head over to the Action Challenge website and register there. Don't forget to tell us too!