BROWN: In today's "Fit Nation," for many of us, the tallest skyscrapers in the world are stunning marvels of architecture. But for others, every big building is just another opportunity to race.</s>DR. SANJAY GUPTA, CNN CHIEF MEDICAL CORRESPONDENT (voice-over): Tower run. It's a growing sport where people race up staircases of the world's tallest buildings.</s>LISA ZEIGEL, PRO STAIR CLIMBER: You have to train to avoid a pain because you're going to feel a lot of pain in a race.</s>GUPTA: Lisa Zeigel ran her first race 15 years ago. Days after September 11th.</s>ZEIGEL: We felt that it was important to show that we weren't afraid. I could only think of the people going down the stairs and the horror of it. But when we got to the top, it was just like no other feeling I've ever experienced.</s>GUPTA: She was hooked. Now at age 57, she's ranked seventh in the United States and 21st in the world.</s>ZEIGEL: The Empire State Building is the ultimate race. You get up into the stairs and you try not to look at the floors. It's just the feeling of accomplishment, just self-affirmation. I would like to keep doing this into my 80s, 90s. I just want to go all over the world and keep doing this.</s>BROWN: That is impressive. Well, coming up, don't miss CNN's Peter Bergen right here next hour with a behind-the-scenes look at his exclusive interview with President Obama airing tomorrow on the five-year anniversary of the raid to kill Osama bin Laden. The president speaks from the situation room about that operation. You won't want to miss the "ANDERSON COOPER 360" special, "</s>WE GOT HIM: PRESIDENT OBAMA, BIN LADEN, AND THE FUTURE OF THE WAR ON TERROR." That's Monday at 8:00 p.m. right here on CNN. We'll be back.
Sky is the Limit for Pro Stair Climbers.