Underground City, Montreal

Listen for a moment. Somewhere ahead, a metro train hums on rubber tyres, a soft rolling sound instead of the screech of steel. Shoes tap on polished stone. A coffee grinder whirs behind a counter. Above you, perhaps, snow is falling on the streets of Montreal, but down here the air is mild and the light is steady. Welcome to the Underground City, the network that locals often call the RÉSO, a play on the French word for network.

First, a small surprise. Much of this underground city is not very deep underground at all. Many of its passages run at basement level, just below the street. Others sit at ground level inside large buildings, or even climb a floor or two. What ties it together is not depth but connection. Office towers, shopping centres, metro stations, hotels, concert halls and university buildings link to one another, so a person can cross a large part of downtown without stepping outside.

The idea took shape in the early 1960s. The starting point was Place Ville Marie, a cross-shaped office tower designed by the architect I. M. Pei's firm, with a shopping concourse beneath it. The urban planner Vincent Ponte pushed a bold vision for the downtown core. He imagined pedestrians moving on a separate level from cars, sheltered from traffic and from the weather. Place Ville Marie opened in 1962, and its lower level became the first piece of the network you are walking through now.

The next big step came with the Montreal metro, which opened in 1966. The city was preparing for Expo 67, the world's fair that brought millions of visitors and put Montreal on the international stage. New stations gave developers a reason to connect their buildings directly to the trains. A tower that linked to a metro station gained a steady flow of people. So the network grew piece by piece, often through private projects, rather than from one master plan built all at once.

That piece-by-piece growth explains something you may notice as you walk. The style changes often. One corridor has warm wood and soft lighting. The next has bright white tile, or a glass atrium full of daylight, or a stretch of plain concrete. Each building owner shaped their own section. Moving through the network feels a little like reading a book written by many authors, each one adding a chapter in the style of their own decade.

How big is it? The figure most often quoted is more than thirty kilometres of passages, linking a large number of buildings and several metro stations. Numbers vary depending on what is counted, because the network keeps changing as buildings open, close or reconnect. What matters for you is simpler. Follow the signs marked RÉSO, and you can travel from shops to offices to concert venues without a coat, even on the coldest day of the year.

And those days can be very cold. Montreal winters bring deep frost, wind and heavy snow. In January, the difference between the street and the corridor can feel enormous. This is the real reason the network matters to the people who live here. Office workers walk from the train to their desks in shirtsleeves. Students cross between buildings with their books. Families shop on a Saturday while a storm blows above them. For many Montrealers, it is simply part of the winter routine.

The metro stations themselves deserve your attention. In the early years, different architects designed different stations, and many include artworks built into the walls, floors and ceilings. You may see stained glass, murals, sculpture and bold abstract patterns. Some stations feel like modernist halls, others like quiet caves of brick and concrete. If you have time, ride a few stops just to look. Each station gives a different answer to the same question: how should a public space underground feel?

Notice, too, the language around you. Signs are in French first, because French is the official language of Quebec. You will hear French at the cafés, at the ticket machines and in the conversations of people passing by. You will also hear English, and many other languages besides. Montreal is a city where people often switch languages in the middle of a sentence. The corridors carry that mix all day long, from the morning rush to the evening crowds.

The network also connects to some of the city's cultural life. Passages lead toward Place des Arts, the performing arts complex where concerts, opera and festival events take place. Other routes reach the arena where Montreal's hockey team plays, and on game nights the corridors fill with fans in red jerseys. Large shopping centres, a central railway station and major hotels also link in. So the same tunnel that carries commuters at eight in the morning may carry concertgoers at eight at night.

Here is a second surprise for many visitors. The Underground City is not one single, continuous mall. It is a set of connected clusters, and some links close at night or on certain days when a building shuts its doors. Getting a little lost is part of the experience, and almost everyone does it. Look for maps on the walls, and keep track of the metro station names. They act as landmarks, much like street corners do above ground.

Critics have sometimes asked whether moving pedestrians underground takes life away from the streets. It is a fair question, and city planners have discussed it for decades. Yet in summer, Montreal's sidewalks, terraces and festivals are full of people. The two levels seem to share the year between them. The streets take the warm months. The corridors take much of the winter. Together they let the city keep moving, whatever the weather is doing outside.

As you stand here, take in the details around you. Feel the warm air from the vents. Watch the flow of people on the escalators, each one heading to a different part of the city. Look at how one building's floor meets the next, sometimes with a small step or a change in colour. These quiet seams mark the joins between decades of construction. When you climb back up to the street, glance back at the doorway. Behind it, a whole other Montreal keeps walking, warm and steady, below the snow.