One thing for sure, Ned Hoelzer knows himself.

“I get obsessed with stuff,” the retired Miami University professor said with a shrug and a grin. “That’s why I never took up golf. I was afraid I’d be obsessed with the game.”

You think?

When he took up chess, he played 300 games the first summer. When he started with ping pong, he played 1,500 games.

He tells you all this while he’s seated behind the desk in his cathedral-ceiling office of his Hanover Township home. If you didn’t know better, you’d think you were in the catacombs of the Smithsonian Institute or an over-stuffed storeroom at Cooperstown.

In front of him, behind him on both sides of him — floor to ceiling — is sports memorabilia.

There is a cabinet filled with baseballs autographed by legends like Mickey Mantle, Joe DiMaggio, Ted Williams, Juan Marichal, Sandy Koufax, Willie Stargell, Frank Robinson, Cal Ripken and Johnny Bench.

There are footballs signed by Anthony Munoz and Ben Roethlisberger, a personalized poster from Evander Holyfield and a basketball bearing LeBron James scrawled name. There are hundreds more autographed items, but the 73-year-old Hoelzer dismisses the spectacle, saying this is nothing but his office.

The sports museum is in the basement.

And just outside — one the second floor of a 21-car garage that looks more like a finely-kept apartment building — is his much-trumpeted model train display.

How’s this for obsession?

The 4,800-square-foot layout took Hoelzer 3 ½, often-painstaking years to build.

There are over 1½ miles of track upon which up to 43 passenger and freight trains wind their way through block after block of cityscapes and over formidable mountain ranges, while passing 1,100 illuminated houses along streets filled with some 1,500 cars.

Hoelzer is opening his train display and sports collection — as well as a game arcade and an art collection — to the public this Saturday and Sunday and next weekend (Dec. 8 and 9) from 10 a.m. to 5 p.m. to raise funds for families affected by Multiple Sclerosis, a scholarship program for the Christian Cooperative Nursery School in Oxford and the Bethel A.M.E. Church in Oxford, which needs a new roof.

This is the fifth year he’s opened his home at 3088 Oxford-Millville Road for charity. In the past, some $40,000 has been raised.

Planning to stop in for 30 minutes or so the other day, I stayed for two hours.

I came across several surprises, including Marilyn Monroe’s 1954 driver’s license — which was issued in the name of Norma Jean DiMaggio — and the original autographed program from the historic 1964 heavyweight title bout between Cassius Clay and Sonny Liston at the Miami Beach Convention Center.

But nothing surprised me more than when one part of Hoelzer’s collection literally came to life in front of me.

Making good on $10 loan

Hoelzer grew up in Sandusky, Ohio, where his uncle ran one of the original Lionel train stores.

By the time he was 8 years old, he not only had his first train set, but had become a fan of the Cleveland Indians, who won the pennant that year.

When he moved to Norwalk to attend high school — and become a multi-sport athlete — his budding obsessions followed, just as they did when he headed to Miami University with his hometown pal, Bud Middaugh, who went on to become a fabled college baseball coach (with 824-319-1 record) at Miami and Michigan.

“Bud’s dad loaned me $10 so I could apply at Miami,” said Hoelzer, who made good on the investment. He got his masters degee at the school and spent over 30 years there teaching accounting and business statistics.

While he’s best known for his model trains, Hoelzer’s sports memorabilia is just as mind-boggling. He has an entire room filled with Roethlisberger and Pittsburgh Steeler mementos. Another houses Cincinnati Bengal collectables.

There are also autographed jerseys of everyone from Kareem Abdul-Jabbar to Nolan Ryan to Brett Favre, a football signed by a Heisman Trophy winners going back to Doak Walker in 1948 and the newest addition, an Urban Meyer signed football from this 12-0 Ohio State season.

Coles coaches again

Talk about life imitating art.

On one wall, Hoelzer has a life-size cutout of Charlie Coles, the recently-retired Miami University basketball coach, as he worked the RedHawks sidelines in his trademark red sweater.

Knocking at the door that afternoon was Coles himself.

He’d come to check in before the charity function kicks off. He is a member of the Bethel A.M.E. church that will benefit from the event.

Coles has not been back yet to see his old Miami team play, but that’s not saying he hasn’t been around college basketball. Nor does it mean he hasn’t resumed coaching.

His son, Chris, is the new head coach of Olivet College in Michigan, so he’s caught some of the Comets’ games. And he coached the Ox City seventh-grade team that played at the Kingdom in Franklin. One of the promising guards he had was his granddaughter, Jazz, just a sixth-grader and the only girl on the boys’ team.

“One day we were driving to a game and she asked me, ‘Are you nervous?’ ” Coles smiled. “I told her, ‘Yeah, I’m as nervous as I got when I was coaching at Miami.’

“She said, ‘Awwh, no way,’ but I said, ‘No, I am and the reason is that you’re on the team. I don’t coach my granddaughter very often.’ ”

Coles said when he was coaching the RedHawks he used to bring his team out to Hoelzer’s place over the Christmas break to see the sports collection, play the arcade games and especially take in the train display.

“At first, those guys would kind of roll their eyes and go, ‘Train?’ ” Hoelzer said. “They were expecting a 4-by-8 layout with one train. But then they’d come up the stairs and their eyes would bug out.

“Everybody reacts the same way the first time they see it. All they can say is ‘Wow!’

“And that’s the part I like best about opening this to the public. I like to see the expressions on the faces of the adults, and especially the kids. And to know it’s helping some worthy causes makes it all the better.”

Turns out obsession can be a pretty good thing after all.