Some 5,000 racers dash to the top of the Colpatria tower in Bogota.
That means climbing 48 floors, a total of 980 steps. Most will make it to the top in 10 to 15 minutes.
The elite athletes, competing for the tower running World Cup, this year held in Colombia's capital, go last. They run the course in about half that time.
Tower running, the sport of sprinting up the stairs of skyscrapers, may sound monotonous and a bit claustrophobic, but it just may be a sport for our times. In an increasingly urban world, running up stairwells is one way to get exercise while avoiding traffic jams, street crime and severe weather.
The first modern tower race was at the Empire State Building back in 1978. Since then, the sport has spread across the globe. Though short, the races are pure torture.
"For a lot of us elite climbers, it's under the theory that if you're not collapsing when you get to the top then you didn't push yourself hard enough," said Kristin Frey, who's from suburban Chicago. Frey is ranked number 2 in the world among women tower runners. Still, she has to pay her own way to races because she can't find a sponsor.
"A lot of companies are like: 'Stairclimbing? You know, we don't want to sponsor stairclimbing.' Because they don't know much about it," Frey said. "They think it doesn't really have a big audience. But some of the races get thousands of participants. But so far no one's biting."
Michael Reichetzeder, an Austrian tower runner who organized the sport's World Cup, said there are certain tricks to winning, like using the railings to pull yourself up the stairs.
"Some athletes can make very good use of it. There are people even who spend hours before in the stairwell measuring out the steps to find the exact way to use the railing. Because if you do it right you can save a lot of energy," Reichetzeder said.
The Colpatria tower is only half as high as the Empire State Building, which stretches up 102 floors. But Bogota's building is especially tough due to the altitude; the city sits 8,600 feet high in the Andes Mountains.
"Obviously, altitude is a factor that helps Colombian runners and hurts the foreigners," said Juan Pablo Rangel, a Colombian who's won the Colpatria tower race twice.
And sure enough, when the elite runners start up the tower, the locals dominate. Angela Figueroa of Colombia wins the women's division, clocking in at 6:32, about 45 seconds ahead of American Kristin Frey.
At the finish line, several runners collapse into the arms of first-aid workers, panting heavily.
Rangel wins the men's race for the third time and sets a new course record of 4:42. Reichetzeder, the race organizer, straggles in several minutes later. But he says just finishing is a victory.
"I couldn't do one extra step. I felt the altitude completely," he said, trying to catch his breath. "So hard. But I did it."