The Tough Mudder Extreme Endurance Challenge is taking place in the grounds of Drumlanrig Castle, Dumfriesshire.
The 12 mile obstacle course is designed by Special Forces to test fitness, stamina and mental strength.
Over 5,000 participants are taking part throughout the weekend, with 100,000 gallons of mud.
On Saturday, participants braved waist high swamps, underground tunnels, fire walking and electric shocks. There are 22 obstacles in total.