Joe Gelmini’s childhood fascination with trains chugged its way from toy choo choos to the real thing. And after a 34-year career in the railroad industry, he has come full circle.

The Fayetteville-based retiree continues playing with trains.

» PHOTOS: Check out the Atlanta and Georgia trains we love (well, mostly)

Gelmini and a slew of others, from saucer-eyed toddlers to senior citizens, will have a weekend-long playdate with model trains at the National Train Show, July 19 through 21 at the Cobb Galleria Centre.

Now in its 23rd year, the show sprawls across 144,000 square feet where hobbyists, some coming from as far as Japan and Australia, shop for toy trains and accessories, peruse a mass of working model train layouts, and chat it up with fellow enthusiasts and manufacturers. It’s the largest show of its kind and the culmination of the annual National Model Railroad Association convention, which Gelmini helps organize.

At the train show his hobby will be in action. Gelmini, an expert N-scale modeler, the smallest of the model-train bunch, will display his work alongside 40,000 square feet of other model train layouts.

These aren’t simply toys zipping around a circle of track. Die-hard hobbyists invest countless hours injecting intricate details, from weathered train cars and spot-on road signs to tiny foliage, bridges and cityscapes. The end result looks as if they’re shrunken versions of the real deal.

Getting up close to these model layouts is the show’s big draw, Gelmini says. An ever-popular attraction is Lego Miniland, a working train layout with everything, including the trains themselves, constructed entirely of Lego building blocks.

Gelmini says many model train enthusiasts are older retired men with enough time and money to invest in their lifelong romance with trains. These are gents such as himself who fondly remember tearing into their first Lionel train set on a Christmas morning years ago. As the hobby advances with time, complete with digital technology and handheld remotes, it simply fuels their passion.

Today you’ll find many young girls and women joining in, Gelmini says. Bringing a model train layout to life requires a wealth of different skills, including carpentry, electrical work and painting. This gives families the opportunity to pool their interests and abilities and learn something in the process.

Of course, you always see a new crop of curious tots with the coming of each generation. The National Train Show feeds that audience, too, with an interactive play area stocked with Thomas the Tank Engine toys, wooden trains, Brio sets and oodles of Lego. Adult volunteers supervise the complimentary kids zone, which gives parents a chance to soak up the additional surroundings.

Grown-ups shop at dealer booths, get the scoop on new products from the manufacturers and have their own model train sets appraised by experts.

According to Gelmini, parents with young ones who can’t get enough of Thomas the Tank Engine should get in line early for one of the show’s biggest attractions. For an additional fee, smaller kids can climb aboard a scaled-down version of a Thomas train and take a ride.

It’s seeing these fresh-faced newbies and their older counterparts keeping the hobby on track that makes it all worthwhile for Gelmini, harking back to that train-induced twinkle he first had in his eye as a 2-year-old.

“I enjoy just seeing people walk away with big smiles on their faces,” said Gelmini, “and maybe with some trains to take home.”

The 23rd Annual National Train Show. Noon-6 p.m. July 19; 10 a.m.-6 p.m. July 20; 10 a.m.-5 p.m. July 21. $12; $11 ages 65 and older; $6 ages 6-12; free ages 5 and younger, and military, Boys Scouts and Girl Scouts in uniform. Cobb Galleria Centre, Two Galleria Parkway S.E., Atlanta. 602-569-9072, www.nationaltrainshow.com.