More than 10,000 people trekked to northeastern Pennsylvania to scale walls, leap fire and crawl commando-style through a mud pit topped with barbed wire.

Willingly. For kicks. And they paid money to do it.

That's obstacle course racing for you: grueling, mud-spattered and, to its legions of fans, addictive fun.

Virtually overnight, obstacle courses have become a favorite diversion of thrill-seekers and weekend warriors. Hundreds of events around the country require participants to go up, over, under and through to the finish line.

Three of the top courses -- Tough Mudder, Warrior Dash and Spartan Race -- expect nearly 2 million runners in 2012.

The races are a novelty, and novelties usually wear off. But promoters insist they have staying power.