They rushed to see some of cycling's biggest names - including four-time Tour de France winner Chris Froome - depart the building before snaking through the streets of Halifax on their way to the finishing line in Leeds at around 4.20pm.
The race was broadcast live in national television. Anneliese Gray, business services manager for Halifax Tourist Information Centre, described how important the event is for the town.
"It's massively important," she said, "people see it on the TV and come here, they come back and visit us again.
"It's great for the town, it's a great atmosphere and whether you like cycling or not, people seem to absolutely love it. Everybody gets involved!
"It does have repercussions later on. People do visit us off the back of this that might not ordinarily visit little old Halifax. It's great."
Among the visitors was 80-year-old cycling enthusiast Richard, who travelled from High Wycombe to stay with Calderdale-based family and enjoy the fun.
He said: "We like the area. My son moved up here a year ago and showed us the Piece Hall, which we think is great.
"And when we heard that the Tour de Yorkshire was starting here we thought, 'wow, we can't miss it!'. It's great for the area."
His son's partner Nicky said: "We have people come from all over the world and the first thing we do is show them the Piece Hall.
"It's fabulous and we're very proud to have it in our hometown."
John Fellows and Paul Bartram are both tenants at the Piece Hall and agreed that the level of coverage that both the race and the Piece Hall itself generates is invaluable to local businesses and to Halifax itself.
John, who runs Mystical and Magical, said: "It's important to have this in Halifax and to put us on the map on a global stage like this.
"For people who have not experienced our town before, or have not been to the Piece Hall before, to have that buzz and vibe that comes from having thousands of people from all over the world here - it's absolutely brilliant."
From The Yorkshire Gallery that he owns, Paul said: "It's not a massive retail day for us personally, but it puts this place out there.
"All the hotels are booked up, all the restaurants are booked up. There are at least 5,000 people here. That's the benefit this place gives Halifax."