I think that the Tough Guy site answers the question best as to what the race is all about:

Tough Guy™ is the nightmare of being chased by a herd of stallions.

Your only escape route is a mighty and revered obstacle course. Built from trees, 15 metres high with Tarzan ropes swinging. No hats and no hook ups. Just pure, organic grip strength from your cold and wet hands.

Belly flop beneath razor wire, the stallions still snorting at your heels, matching your every step. Look deep into the flames before diving through them straight into shoe sucking mud. Then something wakes you, or does it? Were the stallions just a nightmare?

No time to look back, the narrow tunnels beckon. You bravely enter to discover they're filled with murky water. You can't see. You can't breathe. What chance of survival? Grope around and grab that rope. Pull yourself lungs bursting, into the light! You see the sun, or is it just another cruel mirage?

You are faced with a wall climb, as high as a mountain. No visibility again. Is that smoke, mist or cloud? How do you get down? Take the netting or dive into the freezing lake. You suddenly realise that the sound of stallions behind is fading. You must go on. The only route is through the Arctic water.

A monkey rope, a barbed wire crawl, a rubber snake, a skin ripping snake, you can smell the finish. It's familiar.....you recognise.....it smells like.....cocoa! You know you've earned it!