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Just before 3 p.m. on a Saturday, kids line up outside the model train museum, fussing and hopping and peeking inside.

"Thomas is in there!" a 4-year-old boy reports, wide-eyed.

"No way!" his twin brother replies, scurrying over to see Thomas the Tank Engine.

At last, the doors open, and the children — all wearing masks and some clutching toy trains from home — fan out across the Twin City Model Railroad Museum, a place packed with magic and tucked inside an unassuming St. Paul strip mall.

"Oh my gosh, guys, how cool is this?" Kyle Halvorson says to his sons, Ford and Finn. "Is this a touch museum?" he begins warning them, when a man in a canvas apron appears: "Please press the buttons!"

One boy jogs alongside a model train making its way through a miniature Minneapolis. A girl in pink cat ears peers into a nook populated by 2-inch-tall neighbors. Kids run and marvel and press all the buttons. And when they do, things happen — trains whoosh, lights blink and a helicopter's wings spin.

"Look at the big one, Dad!"

This is one way to see the model railroad museum, from 3 or 4 feet off the ground, during the museum's Night Trains weekend events. The lights are low and the displays decorated. Model trains headed across bridges and around buildings create a whirring soundtrack.

By Monday morning, though, the place is bright and quiet. The trains are still, the coffee hot. A pair of longtime volunteers, in their 70s now, have arrived to repair and update what the children don't see — the technology, old and new, that powers these miniature cities.

"We've gotta fix that," Paul Gruetzman says, tapping a track where someone has placed a Post-it with a single word: "Bad."

Tracks must be tended to, locomotives repaired, electrical systems upgraded. Each volunteer has a technical specialty they're known for, a layout they care for. A longtime telephone company technician, Gruetzman is upgrading, wire by wire, the museum's O-scale railroads, in which ¼ inch equals 1 foot, to a new, digital control system.

Gruetzman, 76, has loved model railroads — and the small, detailed worlds they inhabit — since he was 8, when he got an electric train set as a Christmas gift. He ate too many boxes of Grape-Nuts, which he hated, to nab the small train cars inside.

He started volunteering for the nonprofit museum in the 1970s, learning "how to scratch-build from the old-timers." An electric whiz and the museum's unofficial historian, Gruetzman compiled a timeline of its locations and characters that begins in 1934, with the first meeting of the St. Paul Home Work Shop Club: "Five members were present. They began construction of an O-gauge model railroad at those premises."

Gruetzman's own history is tied to that timeline. Giving a tour of the museum's largest, most well-known layout — a panorama of midcentury Minneapolis — he pauses at the Stone Arch Bridge, getting teary. His father, Ray, crafted the bridge in his garage with 3,500 pieces of bass wood and the help of his son and grandsons.

Trains were their shared hobby, he says. "Not very many people end up having a period of time where literally their dad is their best friend."

The Stone Arch Bridge is one of the marquee pieces that made it across town during the museum's 2016 move from Bandana Square in St. Paul to this space on Transfer Road. The new location is bigger, with private space to store, work and build. Backstage, there are hundreds of containers of Lego bricks, sorted by size, shape and color. Donated train sets, sorted by model. A donated N-scale layout in progress, its wood and Styrofoam innards still showing.

Moving here meant dismantling old, intricate layouts. Volunteers strapped the bridge to a snowmobile trailer and, on the drive over, surrounded it with their own cars, says board member Brandon Jutz. Backing it up to the loading dock at the new location, they sighed with relief.

"We were willing to sacrifice our cars for that bridge," Jutz says. "You can't rebuild it again."

The museum has its eye on younger generations. Thomas the Tank Engine brings kids in. But model trains aren't a toy they can play with straight out of the box. The hobby requires reading, understanding, tinkering. Many kids don't move beyond pressing the buttons. But a few always end up crowding Peter Southard's work bench.

On this Saturday, they watch him work on a Lionel engine from 1938. A camera over his head feeds a big TV, showing him, up close, slide off the wheels. His bench is crowded with pliers and screwdrivers, rubbing alcohol and WD-40. In the first half-hour the museum has been open, five people have brought in their old train cars, enlisting his help.

"If you have an issue with a train, I'm not positive I can solve it — but I have a network of other people I can refer you to," says Southard, known here as "The Train Doctor." It's a shorter list than it used to be, he admitted, as folks have retired, moved south and passed on. "There just aren't that many people left that work on these kinds of things."

A retired University of St. Thomas professor, Southard grew up on a farm in Iowa, where his father fixed things. This bench was once his.

Some 25 years ago, Southard came across his brother's Lionel train set.

"I took it home, took it apart and, after a while, figured out how to put it back together again," he says. "I got hooked."

Each size model railroad comes with its own pluses and frustrations. The boxcar in front of him might have a phalange that's worn down, so much that the wheels are catching. Or maybe it's just misaligned. He brings it close to his glasses, grabs a tool from his apron pocket.

A few tweaks later, Southard places the boxcar on the track in front of him, nudging it forward.

"Ah! Success!" he says, smiling. Then he sets it aside and picks up the next one. A model locomotive from the 1950s. A puzzle and a piece of the past. 