So here’s the riddle:

What business makes something big that you see all the time but seldom notice?

These very large, custom-made products are usually unique: built once and never again. Each can cost millions of dollars only to be used briefly, sometimes just for a few hours, then thrown away.

OPINION

Hint: you don’t see their work often because your attention is focused on the people in front of it.

Give up?

Chicago Scenic Studios creates stage sets, museum displays and the physical contours of public spaces at trade shows, conventions, parades, and at least one war.

Their Cermak Road headquarters is an enormous, sleek industrial building, with 165,000 square feet of clean, soaring space that looks like someplace NASA would use to assemble communications satellites.

So big, you hardly notice the 50 full-time employees.

It was started 40 years ago by Bob Doepel, whose flat-coated retriever Remi has the run of the place.

Born in Chicago, Doepel came out of Carnegie Mellon with a master’s degree in fine arts and an interest in theater production. He started at a small theater in Lake Forest, and grew to focus more on arts than commerce.

“So many people do trade shows, we decided we’d rather be a big fish in a smaller pond,” he said. “There are not that many theatrical shops. We do a lot of environmental branding. We do a tremendous amount of museum work.”

Environmental branding?

“We did Halas Hall for the Bears,” he said. “The graphics and branding. Displays, We did inspirational displays, informational displays. The visitors’ center at the Hancock.”

Beth Smith, head of the metal department at Chicago Scenic Studios, uses a water jet to cut through half-inch thick aluminum plate to make supports for a truss arch that will decorate Northwestern’s April 21 Starry Night gala. | Neil Steinberg/Sun-Times

Royal Caribbean cruise lines is replacing the wedding chapels on some of their ships with escape rooms; Chicago Scenic is both fabricating and testing the rooms, using a local Boy Scout troop.

They installed 2,000 bus stop shelters for JCDecaux, the French advertising company that leased them. And constructed six Terra cotta warriors to publicize the Field Museum exhibit.

“We never do anything twice,” said Doepel, 63, leading a tour through the surprisingly massive building, originally a records storage facility for Blue Cross/Blue Shield before everything went electronic.

“Because of the HIPAA [medical privacy] laws, it’s very secure,” he said.

Chicago Scenic built the press briefing center for Operation Iraqi Freedom in two weeks and air-freighted it over.

They did the Cubs victory parade. And the Sox parade. And the Blackhawks parade. Obama’s election in Grant Park.

We walked into the metal fabrication area.

“We’re building a gala event right now,” said Beth Smith, head of the metal department, using a CNC water jet — water with grit in it. The stream, no thicker than a human hair, cuts half-inch-thick aluminum connecting plates that will form a giant truss arch decorating Northwestern University School of Communication’s “A Starry Night” Gala with Stephen Colbert on April 21.

“We can cut almost anything with this,” said Smith. “Glass, Corian, Wood.”

They create both the spaces for international art exhibitions and the artworks displayed in them, with sculptors arriving to oversee  production.

Most of their work isn’t local.

“We just sent an exhibit over to the Olympics in Korea for Samsung,” he said. “It was very technical and very precise and we had no time do it. But we did it. We sent an installer over to put it in and an installer to take it out.”

All of this speed and expertise can be expensive; prices vary according to the size of the job.

“From $10,000 to $10 million,” Doepel said. “We’ve done three Democratic conventions. We did Oprah’s 25th anniversary.”

I didn’t ask, “Which was bigger?” But I thought it.

Few visitors consider the wear and tear on museums. But museum directors do. The American Writers Museum on Michigan has been lauded as one of the best-designed new museums, and credits Chicago Scenic.

“They did all of the fabrication of our space,” said Carey Cranston, president of the museum. “It turned out phenomenally. People love it, how beautiful it is. Their execution, the building of it, was amazing. I’ll have 100 kids in here, they bang the heck out of it and the place is holding up phenomenally. They thought of that, how durable something has to be that’s turned and touched and played with over and over again. “