Competitors ran, crawled and scrambled through the darkness in the 10km Twilight Run at Sibbertoft on Saturday.
The event, at Wrongs Farm, featured hay bale obstacles, muddy slope climbs and water obstacles.
It began as the sun was setting, with many competitors ending the race with head torches to light their way.
People taking part were ruged to raise sponsorship for the Derbyshire, Leicestershire and Rutland Air Ambulance.
It was organised by the same team behind the Avalanche Run in February, which saw 300 runners chase a Yeto across a cross country obstacle course.