At a moment of architectural crisis, Trent University is retaining Canada's modern heritage

In the early morning flurry, snow kisses the brick path and covers the nubby face of the concrete walls as I walk through a narrow passage between two walls studded with stones.

I emerge beneath the rhythmic shadows of a wooden trellis. Nearby, a monumental concrete tower reaches its arms akimbo into the gauzy sky; a few steps away, the Otonabee River burbles softly. Passing through this ensemble of cloisters and squares and flowing water, I could be in another land.

But I'm in Peterborough, Ont., at Champlain College on the campus of Trent University. Its design overseen in the 1960s by the architect Ron Thom, the campus was and is one of the singular places in the country, a crowning achievement of 20th-century Canadian design. This place has been overlooked for too long, but in recent years the university has begun to build on its remarkable original campus – viewing it as a tool for recruitment and seeing it as an asset to be stewarded. This is why I'm here on a quiet Saturday morning to see a masterpiece that's being rediscovered and preserved, an important example for how we will treat our 20th-century heritage.

For the small university, that has meant overcoming some logistical and financial obstacles, says Julie Davis, Trent's vice-president of external relations and advancement. And yet, she adds, "It was clear we had to shine the light on the history and architecture."

Today, Trent is engaged in a careful renovation of its original Bata Library, while new projects – including a new student centre by Teeple Architects – are being guided by attention to the original campus.

In this way, a small institution is setting an example for the entire country: how to retain Canada's modern heritage, which is both critical and in a moment of real danger.

My walk in the snow took me through the heart of Trent's campus, a network of buildings by Thom: Champlain College, Lady Eaton College and the Bata Library. When Thom planned the campus in the mid-sixties, he saw these buildings as the first in a modular plan.

The Faryon Bridge spanned the river, reaching a sciences complex to the east, while another planned bridge would extend the network of buildings to the south.

The campus would be a car-free zone, centred on the river; and all this would contribute to its character as a collegiate university on the scale of Oxford or Harvard.

The new institution was part of a massive postsecondary expansion to meet the baby boom. Across the country, new institutions were being led, and designed, by young idealists; in B.C., Simon Fraser University opened in 1965 with a radical design by Arthur Erickson and Geoffrey Massey.

In Ontario alone, Carleton, York, Waterloo and Trent universities were chartered between 1957 and 1963. (Looking back, Thom would call it "a rapid, almost witless expansion.")

Trent's leadership was, it now seems, preposterously young – the first president, historian Thomas Symons, was barely 30 when he took the job – and idealist. These young academics took the medieval and Victorian precedents for their university seriously. They toured a number of campuses in England and New England, and settled on the college model, mixing disciplines with one another and residence with study, as an antidote to the supersizing institutions of the time. An early planning document insisted the university should "be a place of aesthetic as well as intellectual excitement."

To achieve that, they hired Thom. For its downtown campus, he first renovated and built around a cluster of Victorian houses within Peterborough; then he focused on the main campus as a total work of art, everything from the site plan to the dishes in the dining halls. It was an ideal commission, and Thom – a profoundly gifted designer – was ready.

Trained at the Vancouver School of Art in the 1940s, he had come of age in a small scene of artists and architects who were inventing a brand of modernism suited to the climate, light and topography of the West Coast. "An architect, no less than an artist, should be willing to fly in the face of what is established," Thom wrote in 1962, "and to create not what is acceptable but what will become accepted." Thom and his team built dozens of houses, largely in Greater Vancouver's North Shore.

Thom came east to Toronto with two spectacular academic projects: the Massey College at the University of Toronto, opened in 1963, and then the much larger Trent. When Trent opened in 1967, The Globe and Mail praised it as a "new citadel on the Otonabee," even though it was still under construction; and when it was done a few years later, the campus was being welcomed by students and international critics alike.

No wonder. Thom and his talented colleagues blended careful attention to the site, beautiful materials and fine craftsmanship. The buildings, crafted by Thom's team, including Paul Merrick, are full of complex spaces and details that echo and rhyme with one another. Walking through the original campus is a sensory feast of complexity and nuance; if you ever had the idea that modernist architecture had to be inhumane, this place will cure you of that notion. In the Great Hall at Champlain College, the buttresses and high ceiling make it seem "Hogwarts-like," as one student told me; but the structure is a lattice of very modern concrete that weaves together skylights and wood slats.

Even the landscape, often overlooked in modern sites, has been well conceived. The pathways across campus are paved with an orange brick, which feels right under your feet.

Seeing the campus recently for the first time in years, I was struck by the many different textures of concrete. The variety on Champlain College's exterior walls is known as "rubble aggregate." Hand-sized chunks of local stone were mixed in before workers removed the steel forms and carefully troweled away the surface layer to reveal its mix. This process, meant to be cheap, proved to be preposterously expensive; Champlain reportedly cost $7-million in 1969 dollars. Accordingly, the walls of Lady Eaton College were made of less pricey board-formed concrete. Yet, you can see the marks made by the individual planks in forming the concrete and run your hands over them as you walk through the courtyard that lines the building. This is architecture to lay your hands on.

And it is now in the care of president Leo Groarke. A philosopher, Groarke taught at Trent in the early days, and yet when he returned to the school in 2014, he says, he had to be educated. "I knew it was a beautiful campus, but I didn't appreciate it in detail," Groarke says over tea in the senior common room at Lady Eaton College. We are seated on Eero Saarinen chairs under the waffle-textured concrete ceiling; a set of Jack Bush lithographs line the back wall and a built-in sofa slides under the skylight in the corner. The place is a sixties period piece mixing wood and board-formed concrete, shadow and sunlight, toughness and comfort. What's not to like?

Yet, some of Groarke's precedessors hadn't appreciated the Thom campus much. In the 1990s, Trent's original furniture – classics selected by designer Molly Thom, Ron's wife, or custom pieces by the architect himself – were being discarded or sold in rummage sales. Thom's vision had begun to fall apart in the seventies as public money dried up and enrolment fell. Over time, the university struggled with its finances and the Thom campus – which, Groarke says, "governments soon came to see as extravagant" – became a burden. New additions to the campus took it away from the river and in some cases made dramatic moves away from the original design language; the architectural low point is the 2004 Peter Gzowski College by Stantec and Two Row Architect, which added a big box that is rectilinear and very yellow. How did Trent get here?

"I think familiarity breeds contempt," Groarke explains. "I remember someone saying to me – a faculty member who had been here 25 years – 'I never want to see another beautiful photo of the Otonabee River and the Bata Library.' And I didn't understand that at all. I mean, why not?"

More than anything else, that question is generational. For many Canadians of a certain age, the words "heritage" and "concrete" don't seem to fit together. A massive construction boom that reshaped Canada from the 1950s through 70s, from housing to schools to cultural buildings to universities, hasn't yet received its due. In Winnipeg, the city is aiming to tear down its Public Safety Building; in the Vancouver area, houses by important architects such as Erickson, Barry Downs and Thom are being wrecked to make way for monster homes.

In a sense, there's nothing unique about this crisis. There comes a time for every building that it is too old to be new and too new to be seen as historic.

But the debate about "modern preservation" is largely over in Britain, where preservationists are now trying to rehabilitate 1980s postmodernism. Canada, a country with an uneasy relationship with its recent urban past, remains stuck on the sixties. Former Globe and Mail architecture columnist Adele Freedman was trying to save modernist buildings in the 1980s; not much has changed, as I've learned while following the Toronto school board's decision to demolish an important 1962 school.

And yet, campuses such as Trent form a unique part of our history, shaped by a one-time mix of nationalism, architectural radicalism, gung-ho idealism and – not least – a vast outlay of public money. At Trent, this was the recipe for a masterpiece, and it's unlikely to be repeated.

The proof: Trent's new student centre. The 34,000-square-foot, $16-million project by Teeple Archiects opened this past fall, and by all rights it should be great. It is intelligently planned and interesting in form; it takes formal cues from the existing buildings; its triangular plan responds to the geometries of Lady Eaton College; a hanging stair in the atrium echoes Bata Library; and it opens up to the river, just as its predecessors did. Stephen Teeple and his office have already designed three buildings on this campus, including the spiky Chemical Sciences Building (2004), which embeds itself with care into the middle of the campus.

However, the student centre's façades are factory-made panels of precast concrete, printed with a pattern that mimics the rubble aggregate of Champlain College. It's a clever homage, but a sad metaphor. In the sixties, quality meant handcrafted concrete; now, it means a simulacrum. Likewise, the handsome wood roof beams stop at the façades, replaced by painted steel. The interior of drywall and messy concrete looks, and feels, unavoidably cheap. This is how we make public buildings in Canada today.

To be fair, Trent is not a large or rich institution and its efforts at maintaining its history are exemplary. While other Canadian universities reconsider their modern campus, as Simon Fraser and Guelph are doing right now, they should follow its lead. The university is collaborating with heritage architects ARA Heritage to shape all of its facility decisions; it is raising money toward a Ron Thom endowment to fund the maintenance of its heritage campus; and it has been restoring a series of architectural features, including that trellis I'd noticed and the interior of The Seasoned Spoon Cafe, a student-run eatery at Champlain College.

There is also Alumni House, where I spent the night. Tucked into a corner of Champlain College, it is the former residence for the college's head, and while it's now used partly as office space, it is very much intact. During my time there, I watched the recessed lighting play across the plaster ceiling; I sat and watched the sunlight move across the inner courtyard and ran my hands across the rough concrete walls.

I tried to imagine four years as a student in this place, all the memories that could lodge themselves in my head and my hands. I thought of what Groarke had told me: "Learning to appreciate beauty is its own kind of education."