Sandy Cloutier would feel guilty if after 40 years she closed Allison's Hallmark Shop.

"Maybe I felt like I was doing a service or I was helping because as the stores began to close, they would say, 'Well, I hope you don't leave,' so maybe it's a guilt complex that I have to be here," Cloutier said.

Even as business has slipped for the downtown gift-card shop, today the city celebrates the 40th anniversary of Allison's Hallmark and the snaking, elevated hallway that winds next to it. A lot has changed since the construction of the Holiday Center and the skywalk, opened in 1978. As the halls of the indoor passage have grown, business success has fluctuated.

"There's a lot of reasons why 15 years ago we were doing super good, and then things went downhill," she said, with younger generations using text messages instead of greeting cards and having less interest in knick-knacks.

"When we opened, we were charged the highest rent because according to a UMD survey, it was the highest-trafficked spot in the city."

While today commemorates a historic occasion for Cloutier's business, her challenges and the others that have since closed are not lost on local officials.

"Sure, every business has a challenge of being competitive with online opportunities," said David Ross, president of the Duluth Chamber of Commerce. "And that's a challenge not only for downtown businesses, but for major retailer providers like Younkers in Duluth."

The upcoming closure of the Miller Hill Mall Younkers - and the closure of other local businesses - is part of a larger trend, especially downtown.

"It's a function of how the downtown is changing. A function of the needs of various services," said Elaine Hansen, the director of the University of Minnesota Duluth Center for Economic Development.

While Hansen has talked to some store owners who closed their shops because they weren't interested in working in the business anymore, she says the decline of retail is also a product of people no longer shopping in brick-and-mortar stores.

"Even though the economy is pretty good, how people do business has changed," Hansen said, citing online shopping as a driving force behind faltering local businesses.

Notable businesses connected to the skywalk that have closed over the years include: Bagley & Co., How Sweet It Is and Engwall Peterson Anderson Flowers.

Despite the troubles, Ross says the day should also be celebrated.

"We still have a skywalk system as a strong connecting point as well for businesses in the downtown," he said.

The first section of the skywalk, the Holiday Center, was built in 1978 as a downtown shortcut that would shield pedestrians from harsh Duluth winters. Since then, the climate-controlled indoor route has become a central hub for plenty of other reasons.

"There's a synergy of uses it offers," Ross said. "There will always be a need for the skywalk."

Along with providing access to businesses at the ground level on the main streets of Duluth, it also serves as more than three miles of walkway for people to exercise on their lunch breaks or after work.

The entire skywalk system has gone through several developments since its inception. You can now walk from the Civic Center to the Duluth Entertainment Convention Center, or the public library to Pizza Luce, without having to go outside.

The skywalk system connects many parts of the city, said Kristi Stokes, the president of the Greater Downtown Council. "We truly see (the Holiday Center) as the center of the skywalk system. All parts converge right there. It's the hub of the system."

It also connects several parking garages, enabling drivers from outside the city to use the skywalk as much as local residents.

Meandering around local businesses and busy roads, directional signs called "wayfinding signage" have been put up to help guide walkers. Other signs reading "elevate your experience" shine through overpasses to onlookers below looking to avoid the construction on Superior Street.

"The whole idea is to encourage people to elevate and get around the construction by using the skywalk," Stokes said.

The effort to mobilize people up to the skywalk hasn't gone unnoticed.

"I see more people using the skywalk system because of the construction," said Kristal O'Hara, a cashier at A Time Treasured Antiques.

Another development since its initial unveiling was the start of the Clean and Safe Team in 2005: public employees that monitor the skywalk and the sidewalks beneath it.

"Our entire downtown has gotten better since then," Stokes said. "They are the eyes and ears for our law enforcement and are truly ambassadors for the community."

The city doesn't seem to want to stop expanding it either. While at the center of downtown business, Stokes says there's interest growing east by connecting the Essentia Health campus to the Tech Village. Hank Martinsen, the property services supervisor for the city, says there could be a future in residential use.

"There would be multi-family units downtown," Martinsen said. "Residents will all have access to the skywalk. It's a really good amenity."

"The people who made this decision back in the '70s should be applauded and remembered fondly for such an innovative approach," Ross said. "If you look at healthy, vibrant downtowns like Minneapolis and other communities, you'll see they have properly invested in the skyway system as we have."