It began ten years ago with a couple of friends, some business casual attire, and a desire simply to have fun.
And boy, has it grown.
2017's Tube to Work Day in Boulder was an event. Like, a big event, with people in vests directing tubers, sponsors, live music, waivers, television news stations and participant wristbands.
It hasn't always been that way.
The ridiculously Boulder event brought an estimated 1,000 tubers, dressed in their finest costumes and business casual attire, helmets, and some PFDs to Eben G. Fine Park in Central Boulder early Friday morning.
There were unicorn floats. Floaties. Plaid suits, coffee mugs, GoPros, walrus costumes and taco costumes.
Helmets were required and it's BYOT. (Bring Your Own Tube)
And yes, some of these people really did commute to work down Boulder Creek this way.
PHOTOS: Tube to Work Day in Boulder 2017
It is a celebration of all things fun, wacky, and sustainable. Organizers encourage tubers to take alternative transportation to the park to begin their cold, sometimes perilous journey, down Boulder Creek.
This year's Tube to Work festivities benefited the Boulder Shelter for the Homeless. Organizers and founders Andy Gruel and Jeff Kagan suggested each participant donate one hour's salary to the charity.
At the commute's end, participants were rewarded with free breakfast, live music, and a best-dressed award for one lucky, sopping wet, tube commuter.
It's truly one of those "Only in Boulder" type of events that bring a sort of wacky joy to everyone who sees it, "In the spirit of friendship, community, alternative transportation and goofiness for the sake of goofiness."