Open this photo in gallery The Toronto YMCA on Grosvenor Street. Fiona Spalding-Smith

Don Schmitt exudes quiet confidence as he trots up the stairs of Toronto Central YMCA. Dressed in a navy blazer and an open-collared, light-blue shirt, the eyes behind the thick-framed eyeglasses brighten when he spots YMCA president and CEO Medhat Mahdy. Dressed similarly, Mr. Mahdy extends his hand as his face splits into a wide smile.

After pleasantries are exchanged with YMCA’s vice-president of marketing Nora Gorman and your humble Architourist, a tour of the 1984 facility begins, with Mr. Schmitt taking the lead.

“All the stories I have are of terrifying moments,” he says rather unexpectedly as we stand in the light-filled lobby. “I was completely terrified we didn’t know what we were doing, it was a sort of child’s crusade to do a building.”

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It’s an odd statement coming from such a seasoned veteran. Mr. Schmitt, as architecture aficionados know, is one half of the venerable Diamond Schmitt Architects, and the force behind Vancouver’s Emily Carr University of Art + Design, Lazaridis Hall at Wilfrid Laurier University in Waterloo and the Taylor Institute for Teaching and Learning at the University of Calgary, to name an important few.

Open this photo in gallery Left, architect Don Schmitt, and YMCA president and CEO Medhat Mahdy. Dave LeBlanc/The Globe and Mail

Then again, veterans must start somewhere. In 1980, when he was assigned the task of designing a “new look” building for a modernizing YMCA, he admits he was still a little moist behind the ears: “I’d done a little medical clinic in Quebec,” the 1978 University of Toronto graduate says with a laugh, “and I’d done my sister’s deck” (he adds later that his sister tore down said deck a few months after its completion).

As we walk, however, it becomes apparent that not only was Mr. Schmitt a great architect at the tender age of 29, the Royal Architectural Institute of Canada was correct in awarding this year’s Prix du XXe siècle – given each year to a 20th-century building still used for its original purpose that’s also stood the test of time – to the Grosvenor Street building, which sits near the busy intersection of Yonge and Wellesley streets.

Open this photo in gallery Architect Don Schmitt says the design is intended to create unexpected visual connections, such as encountering the pool when you come in the door. Steven Evans

“This was all about creating visual connection between things, and unexpected things,” he explains. “You come in the door and you’re looking straight through the aqua-fit pool … and straight through the main, 25-meter pool, and there’s a little square window that looks onto Breadalbane Street.

“Or you stand there and you look 90 degrees and you see the Athletes’ Stair,” he continues, “which was just a way of connecting all the athletics in the building, and you can look up and you see that central meeting-space.”

“When I show people around,” Mr. Mahdy adds, “I always tell them there’s a similar, but not as long, staircase in the opera house, which you guys designed as well.”

Open this photo in gallery A long skylight illuminates the towering Athletes’ Stair. Steven Evans

While it would be a stretch to suggest the Central Y is on a par with Diamond Schmitt’s 2006 Four Seasons Centre for the Performing Arts, there is a sense of grandeur that elevates the complex above its workaday palette of terrazzo, stucco, concrete, metal baseboards and wire-mesh windows, which are “really durable and robust,” offers the architect, pointing to hand-applied stucco, and “just like a Roman building.”

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While there are a few nods to the cartoon-Classicism of the postmodern movement to justify that descriptor, such as striped brickwork, glass block and arched windows, what will surely stay with today’s visitors are Mr. Schmitt’s less literal tributes to Roman architecture, such as height, light, air, openness and repetition. For newcomers to Canada, these timeless design moves make the complex easy to navigate; for long-time members, it’s equally easy to catch a glimpse of something completely unrelated to one’s visit, since there are a variety of public meeting spaces throughout.

Design highlights are engineer Morden Yolles’s triangular, board-formed concrete ceiling over the small pool; the vaulted, cathedral-like ceiling over the main pool, which features a tiny round window in each acoustic panel (Mr. Schmitt says that while these add up to only seven per cent of the entire roof, there’s a “great quality” of natural light) and the rhythmic wall-windows that drop to the floor so swimmers can view the greenery of East of Bay Park; and the long skylight that illuminates the towering Athletes’ Stair, where folks often pause to chat on the spacious landings.

Open this photo in gallery The building’s height, light, air, openness and repetition pay tribute to Roman architecture. Fiona Spalding-Smith

Also of note is the second-level, 300-seat, sprung-floor auditorium. With its four sets of massive, custom-made, curved and lead-lined doors, in an instant the room can transform from a quiet chamber music venue to a wide-open, cacophonous space for mingling. “The idea was not to make an auditorium that was tucked down a corridor and locked up,” Mr. Schmitt says. And, finally, the rooftop running track is a treat for its view of the city’s constantly rising skyline.

All of this was built for “eighty dollars a square foot,” says Mr. Schmitt, a touch of surprise still in his voice. “It’s a long time ago, but it was a tough number, even then.”

Open this photo in gallery Many people use the building’s basketball courts. Fiona Spalding-Smith

With thousands of users per day accessing gym equipment, basketball and squash courts, child care, immigrant services, day camps and a 68-student high school for kids with learning disabilities, the building has proven to be extremely successful, durable and adaptable. Rooms have changed function, walls have been removed completely (Diamond Schmitt carried out a small renovation in 2011-12) and a former restaurant is now a flexible community space. In a sense, the building has changed with the city, says Mr. Mahdy, “without losing the heart and soul of who we are.”

“Somehow we got the structure right,” Mr. Schmitt says. “Buildings that are confusing, where you don’t know where you are, are intimidating and, ultimately, not comfortable.

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“It’s a great space for spirit, mind and body.”

The Prix du XXe siècle is being awarded at the RAIC Festival of Architecture in Saint John on June 1.