Marathon world record holder Eliud Kipchoge will make a second attempt to run the distance in under two hours in Vienna, Austria, on Saturday.
The Kenyan runner, who ran the marathon in two hours and 25 seconds in his first attempt, told BBC Sport Africa he'll feel like the first man on the moon if he does it.
The assisted conditions mean it will not be a world record if he succeeds. Kipchoge's world record is two hours, one minute and 39 seconds.
Watch live coverage of the 1:59 Challenge, Saturday 12 October, 07:00-09:30 BST on the BBC Red Button, BBC iPlayer, BBC Sport website & app (UK only).