NEW YORK — Adam Ottavino never expected The Lab to turn into this.

The New York Mets reliever just wanted a place in the city to throw in the offseason, something that can be hard to find here in the winter months. Heading into the 2018 season, Ottavino — then with the Colorado Rockies — converted what used to be a Nine West shoe store underneath an abandoned Chuck E. Cheese on St. Nicholas Ave. in Harlem into an advanced pitching facility, decked out with cameras that measure pitch spin rates and iPads that provide pitchers with instant feedback.

“We were just trying to make the most of the situation,” Ottavino said.

Ottavino — who grew up in Park Slope, Brooklyn — rented the retail space from his father-in-law hoping to find a temporary place to throw his bullpens after dropping off his two daughters at school. Five years later, The Lab welcomes everyone from college pitchers to minor leaguers to amateurs from New York’s men’s leagues, right on up to Ottavino’s fellow big leaguers — free agent hurler Matt Harvey, Chicago Cubs starter Jameson Taillon and Yankees reliever Michael King are among those who have made appearances.

“It wasn’t meant to be this way,” Ottavino said. “But I started realizing this was gonna be about more than me. It was gonna be about the whole New York City baseball community. Trying to be a resource for guys.”

To take The Lab to the next level this offseason, Ottavino hired staff to help run the facility for the first time, bringing in Gerardo Roque and Jason Pastuizaca — who both work in the Mets clubhouse. The space now resembles a baseball museum, curated by Ottavino, with autographed baseballs he’s collected throughout his career, including legends like Lou Brock, Ichiro Suzuki and Whitey Ford. There are autographed jerseys of some of Ottavino’s teammates over the years, including Scherzer, Jacob deGrom and Nolan Arenado.

“Every time I come here, there’s something new,” Taillon said. “It’s just good vibes. This is all you need for guys who know what they’re doing, know how to work. There’s a group text and whenever I signed my new contract, I didn’t have like 90% of the numbers saved in there, but everyone was congratulating me.”

There are name plates for everyone who regularly pitches in the facility, a cork board with Polaroids taken by Ottavino inside The Lab, and a white board tallying the number of bullpens thrown by each pitcher, the top velocity thrown at The Lab (94.7 mph by King last winter while building up to full strength ahead of spring training) and a quote of the day, recently featuring a line from former United States secretary of defense Donald Rumsfeld.

“There are known unknowns, things we know we don’t know,” the quote reads. “There are known knowns, things we know we know. Are there unknown unknowns? Things we don’t know that we don’t know?”

The community has grown steadily over the years, according to Alex Katz, who was one of the first people to use the facility when it opened. Katz — a friend of Ottavino who played in the Chicago White Sox, Baltimore Orioles and Cubs systems and runs the cleat customization company Stadium Custom Kicks — hopes to pitch for Team Israel in the World Baseball Classic, and uses The Lab to track his bullpen progress while getting advice from current big leaguers.

“It’s priceless, invaluable,” Katz said. “[You] can’t spend hundreds of thousands of dollars and get info like this. You can talk to guys who made All-Star teams. You can’t beat it.

For some in The Lab community, working alongside big leaguers like Taillon and Ottavino preparing for a season is inspirational. John Lynch, a junior at St. Joseph’s University on Long Island, got his first close-up exposure to major leaguers after an invite from Katz.

“You look at yourself and you look at them and they were in your shoes at one point and they’re just people,” Lynch said. “I’m one of the younger guys here and I’m just soaking it all in.”

For Jake Jaffee — a model who’s worked with Supreme, Harley Davidson and North Face and plays in his free time for the Hudson Hurricanes of the New York City Metro Baseball League — spending time in The Lab around major leaguers reignited his passion for baseball.

“I’ve gotten a whole new appreciation for what the players go through,” Jaffee said. “It’s surreal because you’re lucky to see a guy hitting 86, 87 in the men’s league, but to actually see up close 92, 93 and see the nuances of how guys pitch, you don’t get that inside scoop every day. It’s such a treat.”

The Lab also provided a place for pitchers to throw during last winter’s lockout when they were unable to use their teams’ facilities. King and current free agent reliever Luke Farrell both took advantage of The Lab during this period.

“It’s fun for me because you see them up close and make relationships out of it,” Ottavino said. “At the same time, it’s cool for them because they know they have a place they can come and be with their kind of people.”

Ottavino does not anticipate The Lab going away any time soon. The 37-year-old just signed a two-year, $14.5 million contract to return to the Mets, and said he’s noticed a connection between his performance and working in The Lab.

“My three best seasons are after I’ve worked out here,” Ottavino said. “I don’t know if that’s a direct correlation, but it’s pretty strong. It’s so hard to throw when you’re relying on others but when you have your own situation you can throw whenever you need to, work on getting better.”

That opportunity to get better with access to a lot of data is what appealed to Taillon, who is adding a sweeping slider to his pitch repertoire this offseason while finishing out his lease in New York after two seasons with the Yankees. The Trackman data has allowed Taillon to work on his release point and get instant feedback on how the ball is coming out of his hand.

“Plus, Otto is just a walking baseball encyclopedia,” Taillon said. “He’s probably better than 99% of pitching coaches in the league.”

For Ottavino, The Lab turned into the manifestation of a childhood dream, a place to create a community around the art and science of pitching.

“I know that if I were a younger guy and I had an opportunity to watch some major leaguers grow and talk to them and pick their brains, I would have loved that as a kid,” Ottavino said. “That would’ve carried me a long way into working hard every day towards my dream.”

Ottavino never expected that dream to come true in an unmarked Harlem storefront, but where The Lab is located doesn’t matter.

“You could put us in the middle of a freaking desert,” Taillon said, “but if we have this information and have this camaraderie, conversation, we’ll find a way to meet.”