Ironman triathlon: Three grueling races in one

Cambridge, Maryland (CNN)Swim, bike and run. In that order. And that's basically it. The deceptively simple idea for the popular sport of triathlon is built upon a triple challenge that pushes one's body and mental perseverance to reach beyond a single discipline.

And "tris," as its athletes call them, are now so popular -- with roughly half a million participants each year -- you could say that triathlons are the new marathons.

Cambridge, Maryland (CNN)Swim, bike and run. In that order. And that's basically it. The deceptively simple idea for the popular sport of triathlon is built upon a triple challenge that pushes one's body and mental perseverance to reach beyond a single discipline.

And "tris," as its athletes call them, are now so popular -- with roughly half a million participants each year -- you could say that triathlons are the new marathons.