Around 40,000 runners walked the streets of downtown on Sunday morning for Hot Chocolate 15K and 5K.
It's called "the sweetest race in the United States" and one of the founders, Steve Ginsburg, says he and his staff started the race nine years ago to organize an event after the Chicago Marathon.
There was no race at the time, he says, so he and his team thought about a good topic and chose chocolate.
Part of what makes the race unique is the fact that runners in Grant Park are celebrating eating chocolate sandwiches. It's also unique because the race is the first after the Chicago Marathon.
The race benefits Ronald McDonald House Charities.
"We are really proud to organize a great marathon race," said Ginsburg. "Runners feel safe... everyone can run at his own pace, even with so many people."
The race started to go to other sites as it grew.
"At one point it was literally the fastest growing race in the world," he says.
Now it is in 16 cities. The Hot Chocolate breed grew from 3,500 to just under 50,000 in five years in Chicago, Ginsburg added.