CHICAGO (CBS) — For 50 years, Stuart Grannen has traveled the world, looking for unique antiques.

“It’s a treasure hunt every single day,” he said.

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His company, Architectural Artifacts, has been in business for 25 years in a refurbished century-old building in Chicago’s Ravenswood neighborhood. It’s crammed from floor to rafters with antiques.

“Oh, we’ve got at least 10,000 pieces here. Most of those are big objects. There’s 80,000 feet – it’s the biggest store in the world,” Grannen said.

Among those items: windows by Frank Lloyd Wright, artifacts from Louis Sullivan-designed buildings, and the columns from the old Mercantile exchange.

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“We went up and we got those – 17 stories up. The building got taken down by hand so each day, we would be out there. As the building got lower, we could get another piece of the column,” he said.

What distinguishes an antique from a piece of junk?

“It all starts with quality. It has to have been a quality piece when it was first made and made well, made to last and made beautifully,” he said.

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To mark the 25th anniversary of Architectural Artifacts, Grannen plans a three-day auction at the facility at 4325 N. Ravenswood Av., from April 5-7.