As the new Highway 99 is nearing it’s full operational days, Seattle had two waterfront highways full of pedestrians.

Thousands of people gathered at downtown Seattle on Saturday, traveling on foot through the new Highway 99 tunnel and taking a last stroll on the aging Alaskan Way Viaduct.

The tunnel was open on Monday to car traffic finally ending the viaduct replacement story which has been in the place for the last 18 years. It officially swapped Seattle’s decrepit elevated highway with a gleaming new subterranean one.

Initially, the crowd of pedestrians moved to savor the rare chance to experience automobile infrastructure on foot, just once before the tunnel opens for cars, and only once before the viaduct comes down forever.

About 100000 people roamed through the structures, marching south through the new tunnel and, like a river eddy, flowing back north on shuttle buses and along the viaduct. And around 30000 people did an 8K run/walk Saturday morning, and 70,000 people walked the viaduct and the tunnel, the state Department of Transportation said.

A line to enter into the viaduct at Seneca Street stretched the length of four city blocks and lasted an hour.

“It’s part of Seattle; it’s been there as long as we’ve all been here,” said Brian Hosack, of SeaTac, waiting in line on First Avenue. “It’s one of those events that is semi-once-in-a-lifetime.”

Instead of cars and bigger vehicles, the viaduct carried 90000 people daily before it was closed recently. The elevated highway was having loads of people, filled with temporary art exhibits and Seattle esoterica. People took photos of the highway, the waterfront, the ferries, each other. There were food trucks selling espresso and Taiwanese bao. Musicians — a bass and guitar duo, a band of banjos and ukuleles — played. There was also a sockeye salmon mural and a giant owl puppet. A line of vintage trailers was also there recording people’s memories of the viaduct.

Sue Duvall, of Seattle, noticed walking for the last time things that she never did while driving. Things like, potholes, outlined in neon spray paint, the backside of Pike Place Market, intricate little urban scenes — the spaces between buildings and beside stairways — that get swept away at the speed of a car.

But the things that people always mention about the viaduct are common.

“It was just like my last drive, a few weeks ago,” Duvall said. “A tear welled up in my eye. And it’s weird because it’s an ugly, ugly, ugly piece of road.” She gestured at the slate-gray sky. “But whether it was like today, or bright, blue, sunny skies, it would still stun anyone who saw the view for the first time.”

People roamed through the Battery Street Tunnel, which closed to cars forever Friday night and will soon become the final resting place of the viaduct’s rubble. It was dingy and full of graffiti (messages ranged in profundity from “your money enslaves you” to “I love tacos more than you!”), and it formed a stark contrast with the $3.3 billion new projects that will replace it.

The new project’s walls are pristine white having green characters every few hundred feet, pointing the distance to the nearest emergency exits.

“It’s so well lit,” said Amy Stone, of Seattle, after walking out the south end of the new tunnel. “It’s bigger than I thought it’d be.”

At the official inauguration ceremony, dignitaries recounted the eight years of planning and discussion that led to choosing a tunnel and the ten years of fitful engineering and construction that led to its completion. They appreciated former Gov. Christine Gregoire, who decided the deep-bore tunnel in 2009 and praised the workers and agencies that got it built before an earthquake destroyed the viaduct.

“I am going to outlive the viaduct, and it is going to come down while I’m still standing up,” Gov. Jay Inslee said. He even went on comparing the new tunnel to the Eiffel Tower, the Pyramids, and the Taj Mahal.

“There are many wonders in the world,” Inslee said. “We have the Seattle tunnel, the eighth under of the world.”

But, there were critics of the whole new project present in the ceremony. Former Mayor Mike McGinn, the tunnel’s most-prominent opponent, stood in the crowd but declined an offered spot on the dais. McGinn long argued that we shouldn’t build new highways that aggravate the climate crisis.

“I don’t know what we’re celebrating,” said McGinn, his pant-leg cinched by an elastic cord, to stay clear of bike gears. “I’m kind of down here to see if anybody’s going to say ‘climate.’” (None of the 10 speakers said “climate.”)

But, mostly the day was jubilant and memorable as the city is welcoming a new construction.

“It’s an engineering marvel; I’m glad they built it,” said Jim Danninger, of Kirkland. “It’s a huge achievement.”