It was, said one competitor, like going to Hell and back. Before being allowed to take part in the 11th annual Tough Guy Sunday ,each entrant had to sign their own "death warrant" - a disclaimer that said: "It's my own bloody fault for being here."
This was an assault course capable of grievous bodily harm. The 4,000 male and female entrants faced a 40ft underground crawl through the Vietcong tunnels, walking the plank across a fire pit in the Killing Fields and enduring the Bathead Swamp - an 800m walk up a muddy canal, chest deep in water.
Marshals dressed as commandos fired machine-gun blanks and let off thunder flashes and smoke bombs as the mud-caked volunteers scrambled under a 70m section of barbed wire just 18 inches above the ground in the Stalag Escape.
Teamwork was needed to negotiate the Elephants' Graveyard - three seven- foot deep pits which competitors have to jump into before enlisting a friend to help them clamber out.
But nearly everyone agreed that the worse part of their ordeal was diving three times through a freezing water tunnel.
"My legs just cramped up like sticks," said British Aerospace fitter Trevor Bowden, 33, from Stockport. "You are totally submerged and have to dive under two telegraph poles. When I came up I was so cold I thought my head was going to explode."
Standard kit for the race was a thermal vest, Lycra shorts, fell boots and a bobble hat. Most competitors arrived at the finish shivering so uncontrollably that they spilt almost every drop of a cup of tea they were given to warm up. "I trained for this event by jumping into icecold waterfalls in the Brecon Beacons but nothing prepared you for this," said Warwick University student Zig Mortimer, 23.
"I could feel my heart beating in my head after I dived through the underwater bridge. Sheer willpower drives you to keep going through all the pain. It's a very unusual experience.
"Someone got stuck inside the Vietcong tunnels. His shoulders were just too wide to go through and everyone behind was trying to drag him out. My whole body is still shaking now."
Tracey Baxter, 27, a Norwich printer, said: "It was absolutely horrible. Crawling through the tunnels was so claustrophobic it made me cry. I couldn't feel my hands because they were so cold and I think the fire pit was there just to warm you up."
Diane Mort, 38, from Swansea, a legal executive, said: "I've lost all feeling in my right leg. I was reduced to tears at one point - I just couldn't believe I was doing this."
The eight-mile course was built by the event's organiser Billy Wilson on a 600-acre farm near Wolverhampton. Mr Wilson, who runs a rescue centre for horses, said: "We advise people to train for this event by strapping themselves to the bonnet of their car and getting their wives to drive them through the car wash. I have pictures to prove people have tried it.
"What we are doing is testing people to the limits of their endurance and fear of natural things. We are trying to re-create the First World War and Vietnam battlefields to show people what their granddads went through.
"You can imagine the adrenalin rush when they climb over a 320ft-high rope ladder called the Behemoth and see these fire pits. The only way across is over three pathways made up of a nine-inch-wide plank. There ain't nothing like this in the world. You can't get this thrill watching Arnold Sch-warzenegger's stunt man at the cinema.
"Women seem to come out of it less stressed and knackered than the men because their bodies don't collapse so quickly. Four people suffered broken legs last year but we've never had anyone die on the day."
Around 150 people were treated for hypothermia and two taken to hospital, one with a suspected broken thigh.
Margaret Coomby, the St John Ambulance controller, said: "It's been like battlefield conditions here. Some people were too cold to shiver. They couldn't help themselves and they couldn't even walk, so we wrapped them up in blankets and gave them plenty of warm drinks to help them recover."
The winner - for the third successive year - was Aled Rees, 26, from Cardiff, in a record 1hr 35min 47sec. The stragglers took more than five hours but all 2,900 who completed the course received a medal, because if ever there was an event where the taking part was as important as the winning, this was it.