The annual Relentless 24 mountain biking endurance race kicks off at noon on Saturday (10 October) at Nevis Range, near Fort William.
The winner will be the rider who completes the most laps of the course, which threads its way through Leanachan Forest in the shadow of Ben Nevis.
Frazer Coupland, of event organisers No Fuss Events, said: "With the huge diversity of routes available to us we have conjured up another cracker this year. It includes sections of the World Cup Witch's Trail and even some sections from the first Relentless back in 2006.
"The technical climbs are hard but fair and there are brilliant singletrack descents as a reward. I am so chuffed with this year's course I have entered a team myself. Why should I miss out on all the fun?"
Following a Le Mans-style racing start, up to 300 riders will battle it out until noon on Sunday. With at least half of the event taking place in the dark, the course has been designed to be rideable for the full 24 hours, regardless of weather conditions.
You can take part solo or as part of a team of two, three or four. Entry costs £40 and registration will be accepted up until the morning of the event. For more information, visit www.nofussevents.co.uk.