DENVER -- At first glance, the four women with their heads bent over crochet hooks may appear to be an old-fashioned sewing circle.

But in reality, they are an anonymous, underground group of Denver street artists whose covert crochet work is already all over the city. From tree cozies to bike rack wraps, it's called "yarnbombing," and for almost three years, the Ladies Fancywork Society has been showing Denver a softer side to street art.

They meet every week with food, drink and street names -- after their grandmothers.

"We're crafters. We're artists and this is our city. We just want to be a part of it," said one yarnbomber who goes by Esther. "Esther isn't the toughest street name out there."

But after years of doing small pieces scattered around the city, the time has come for the Ladies Fancywork Society to take its tagging to the next level with their largest, most visible yarnbombing ever.

"It's taken a couple of months of planning, a month of crocheting," said "Lucy Lynn."

7NEWS went along for the ride at three in the morning to the "Dancers" statue outside the Denver Performing Arts Center. The group brings along crocheted legwarmers that measure seven feet by seven feet, and in a matter of minutes, they're on.

"Guys, they look awesome," said "Maxine."

But as often happens with this type of art, when the sun came up, groundskeepers took it down.

"It's more about how much fun we have doing it and seeing it up," said "Lucy Lynn."

Plus, "Esther" said, they already have big plans for more big projects.

And, they'll be doing it "as long as we have yarn and hands to crochet with."

So stay tuned, the Ladies Fancywork Society will strike again.

Some critics have called yarnbombing vandalism or littering.

Denver police said investigating yarnbombing is not a top priority, especially since no property has been damaged. But they said if someone complains they would have to look into it.

So far, no one has complained.