Chris Warner, one of the world’s most accomplished alpinists, has a plan for the country’s growing number of abandoned big box stores: climbing gyms. And he’s starting with the headquarters of what was once the nation’s largest sporting goods retailer.

“We have been seeking out those kinds of spaces forever, and almost always landlords wouldn’t even want to hear our pitch.They were intrigued by our use, but they couldn’t get past the fact that we weren’t as a good of a credit tenant as, say, a Best Buy or something,” Warner said. “Now they look at those kinds of places thinking they don’t want to sign a lease because they are probably going to be bankrupt in two years. Now they are saying, ‘Well, let me get this knucklehead climbing gym guy instead.’ ”

Warner’s Earth Treks, with climbing centers in Virginia, Maryland and Golden, is beginning construction of a climbing gym in the sprawling former Sports Authority headquarters in Englewood, at the corner of Hampden Avenue and South Santa Fe Drive. When it opens this year, the 52,000-square-foot climbing and fitness facility will be the country’s largest indoor rock gym.

Denver’s Etkin Johnson Real Estate Partners announced this month it had sold the two-building former corporate headquarters to Ogilvie Properties’ West Hampden Investors for $15.8 million. The commercial real estate firm purchased the property in 1998 and leased both buildings to Sports Authority from 2001 to 2016. Earth Treks is taking over the building at 1050 W. Hampden Ave. CBRE Group Inc. represented Earth Treks in the lease negotiation.

With a recent infusion from New York private equity firm Tengram Capital, Earth Treks is pursuing aggressive expansion plans. Warner wants to increase the number of Earth Treks gyms in the Washington-Baltimore region to 10 from four, and he imagines “five or six” of gyms along the Front Range.

“From there we want to go into new markets,” he said.

Repurposing big box stores, which are fading at a breakneck pace, is a mounting challenge for the retail industry, where hundreds of the suddenly empty stores anchored thousands of peripheral businesses.

CBRE, the world’s largest commercial real estate investment firm, noted in its 2017 market report that 70 big box spaces are available for rent in metro Denver.

“Looking ahead, developers and landlords are expected to create new developments and reinvest into upgrading spaces in an effort to make them more attractive to retailers and the consumers seeking innovative experiences,” reads the CBRE 2017 Market Outlook report for Denver.

Englewood last year fretted the impact from the demise of its second-largest employer. Sports Authority had been in the location since 2003, when it merged with Gart Sports, which had occupied the space since 2001. The campus was home to 772 employees when Sports Authority filed for bankruptcy protection a year ago.

The ideal solution for Englewood would be “to replace those jobs with an equal number of jobs,” said Brad Power, the city’s director of community development. But luring a major employer is not an easy task. A climbing gym might be unexpected, but if the new Englewood facility draws visitors like the Golden gym — which regularly hosts 1,000 visitors a day — the businesses around the bustling corner could benefit.

“Anything that draws from a regional perspective is a good deal. Hopefully this will put that site on the map,” Power said. “If it’s not a job center moving forward, if there’s something that can engender more people coming to the site and more people gathering around the site, we will be happy. It makes sense this could be positioned as a big draw for folks.”

Warner left in late March on an expedition to scale the world’s third-tallest mountain, the 28,169-foot Mount Kangchenjunga on the border between Nepal and India, where he could become the second American to summit the four tallest peaks in the world after Ed Viesturs.

A decade ago, Warner had a thriving guide business, leading expeditions and hosting leadership seminars based on his history as one of America’s most accomplished mountaineers. He has led more than 200 expeditions, and is one of only 11 Americans to summit both Mount Everest and K2.

In 1997, he was pinned at 14,000 feet in a blizzard on Alaska’s Denali with a client, a real estate tycoon from New York. They spent a week in the tent. After running out of things to talk about, Warner mentioned his dream of opening a climbing gym on the East Coast. The two sketched a business plan on toilet paper.

“I shoved it all in a Ziploc and the guy said if you can get me out of here alive, and you can pay me back in five years, we will make this work,” he said.

Two years ago Warner shut down the guiding business and started focusing exclusively on his climbing centers, which were rapidly evolving beyond gyms catering solely to climbers.

Back in the day, rock gyms were typically founded by climbing bums who wanted a place to train. They were filled with athletes aspiring for big projects, and the vertical walls of man-made holds were testing grounds. Now those gyms have grown into gathering places, with workout equipment, yoga rooms, training areas, meeting rooms, coffee bars and bustling retail counters.

“It’s not just about climbers anymore,” Warner said. “Some of these people might never go climbing outdoors at all. We used to build the outdoors indoors and now we think about what would be super cool to climb. With some of these kinds of designs, we are really creating a giant piece of art and you want to climb the art.”

Warner points to a gaggle of 20-somethings crowded around a route, one of 400 in his 29,000- square-foot, $6 million gym in Golden, built on property he bought in 2012 from a developer who had planned to build a hotel on the spot across from Jefferson County’s Taj Mahal government center. The group is cheering a man dangling above. He is clinging by his fingertips and preparing a dynamic leap to an overhanging hold a few feet above him.

“Not one of them has a cellphone,” Warner said, noting that the gym in January hosted more than 20 days with more than 1,000 customer check-ins. “That is our demographic right there.”

Earth Treks ranks as the country’s top climbing gym retailer, said Warner, who expects to sell close to $2 million in climbing gear at his five gyms this year. Those sales have grown more than 20 percent a year since 2010, he said.

The retail growth mirrors a national trend that has climbing sales — gear, shoes, cams, ropes and helmets — as one of the strongest areas in sports retail. The NPD Group, which measures retail trends across the world, released a report last month showing climbing sales reaching a four-year high of $175.5 million in 2016, up $52.9 million since 2014. That ranks as one of the fastest- growing retail segments for any outdoor sport, said Matt Powell, sports industry analyst for the NPD Group.

With climbing debuting in the 2020 Summer Olympics in Tokyo, Powell expects the retail and participation growth should continue.

“In my opinion, this is an outgrowth of millennials wanting to stay fit and having fun doing it and wanting to share that experience with their friends and indoor climbing gyms allow them to do all that stuff and have beer as well,” Powell said. “The question is how long will it last? Is Top Golf or some activity the next hot thing? I don’t know, but right now, there’s no question there is a lot of heat around climbing. But I think developers with those large properties want to be very careful here to make sure this isn’t a flash in the pan.”