There's a free marathon happening in London this autumn (but it's a secret)

For those all too familiar with the London Marathon ballot rejection letter, there's an alternative new race in town that could give the city's best-known 26.2-miler a run for its money. The Secret Marathon is a bit hush-hush, but what we do know about this free mystery event is that it's popping up sometime in autumn, somewhere in the city, and you won't need to enter a ballot to get involved. And it seems we're digging it: over 10,000 people have already signed up, so if you want to try your luck, you have until the end of May 6 to enter. Find out (a little) more at secretmarathon.com. 

Fancy a challenge? Here are three fun running events worth training for this summer.