It's the tallest indoor stair-climbing event in the world, and it is all for a great cause.
About 2,000 people took part in climbing the 103 floors to the top of the Willis Tower during Sky-Rise Chicago Sunday.
It's not just for the good athletic effort, but rather it's all to raise money for the Shirley Ryan AbilityLab, a research hospital helping those with rare conditions or injuries.
"If you've had a stroke, brain injury, spinal cord injury, some kind of trauma, and you need to get better, this is the place to go," climber Mack Reynolds said.
Amber Macia's daughter also spent time at the AbilityLab.
"To see everybody here for her every year. It's for her legacy. It's her legacy every year," Macia said.
The people at the top make it all worth it, as they cheered the runners on. And the view isn't half bad either.
Read more at WGN 9 Chicago.