You'd have to be crazy to tour wintry Toronto without a coat on. Crazy like a mole.

For two days, I was that creature. Forgoing fresh air, traffic and outerwear, I moved into Toronto's subterranean city. The 16.7-mile stretch of walkways, called the PATH, lies below the downtown financial district and is insulated from any mercury drops. Sticking to the netherworld and its adjoining street-level atriums and skywalks, I was able to shop, eat and even sleep without losing feeling in my face.

Indeed, while others suffered in 14-degree weather, I was enjoying lovely conditions: clear and cloudless in the 70s, with not a hint of precipitation.

"It's really a world underground," says Sousie Tsotskos, a spokeswoman for Tourism Toronto. "Some people go to work, go out to eat, go shopping, go to the cinema, see a hockey game -- and never have to go outside."

Toronto residents have good reason to stay indoors. In February, the city's average temperature is 23; in March, it jumps all the way to 32. Days before I arrived, the city was under a "cold alert," which warns folks to limit their outdoor exposure for fear of frostbite.

But don't let the inclement weather scare you off Toronto. There's an alternative -- if you can exist without natural light.

* * *

Toronto's first pedestrian tunnel appeared in 1900, when the major department store T. Eaton Co. connected three of its properties. In 1917, five pathways were added. Ten years later, the Royal York Hotel (now the Fairmont Royal York) and Union Station were linked, allowing refined patrons to travel from the train depot to the haute-class hotel without mussing their coiffures. The PATH really burgeoned in the 1970s, when a connector was constructed between the Richmond-Adelaide and Sheraton centers, two hives of activity.

Today, the PATH links more than 50 buildings and office towers, many bank- or finance-related, and features more than 1,200 stores and businesses, including boutiques, spas, restaurants and hotels. It also offers access to a number of subway stations and some of the city's bigger attractions, such as the Hockey Hall of Fame and the Roy Thomson Hall, a performing arts venue.

The Ontario capital isn't the only city that keeps you covered. Other urban areas around the world, especially those that suffer from debilitating heat and/or cold, have similar setups (see box below). The sealed environments are heavily used by residents and visitors. PATH manager Michael Saunders says more than 100,000 commuters use the system every weekday; on weekends, about 10,000 tourists and weather-sensitive locals wander through the labyrinth.

At first blush, the PATH seems user-friendly. Though the system is not an exact twin of the above-ground grid, it does identify the streets and buildings above; walkways vary from mall-like corridors to ornate bank lobbies to skyways with snatches of sunshine. Color-coded signs lead visitors through the maze. Theoretically, you just have to know your yellow from your blue.

In reality, you need to have an internal GPS. The system seems to have been devised by a drunken urban planner. It wanders and zigzags, then dead-ends before stumbling off in some other direction.

"Those colors -- they're just colorful," said the Hilton reservationist who checked me in after I spent an hour looking for the hotel, which can be accessed underground through Adelaide Place. "Sometimes I have to go outside, look to see where I am, then run back inside."

The system's northernmost reach is the Toronto Coach Terminal, the city's bus depot; its southernmost is the Air Canada Centre, home to the beloved Maple Leafs hockey team. Other points of interest sit along the eastern and western fringes, such as the Canadian Broadcasting Centre and the Metro Toronto Convention Centre.

The good news: The PATH is set to expand. The bad news: The PATH is set to expand.

Saunders says plans are in the works to bridge the new Four Seasons Centre for the Performing Arts as well as the Ritz-Carlton, still under construction. "We're going to add another mile," he said. "But we're not trying to have the longest one in the world. We are trying to keep it compact around the financial district."

Confoundingly compact, that is.

* * *

Like a true pioneer, I set out on an exploratory mission, starting in Union Station, so big and obvious even I could find it without stopping every third person for directions. From there, I decided to head west (or orange) to visit the CBC's museum.

Since it was the weekend, the "streets" were fairly deserted, and many of the shops were closed. Occasionally, I passed other people, often couples or small groups of friends off to shop or catch the subway.

I also glommed onto a lot of people in an effort to get un-lost. Those included Brenda, who worked in the area and was taking advantage of her free parking spot for the weekend. "We use the underground even though it takes longer," she said. "We use it to go bar-hopping." I later saw Brenda milling around confused, and you couldn't blame the alcohol. "See, we get lost, too," she admitted, before giving up and exiting.

Even following the map religiously can lead to miscues if you take an escalator by mistake or pass by what appear to be off-limits metal doors. (Many of the passageways that cut through buildings lead to closed doors. Open them; it's allowed.) I was two corners away from my destination when I hit a hard obstacle: a locked door with a sign saying there was no access because of Ritz construction. I had two options: Abort plan or bolt across the street, sans coat.

Guess which way I went.

As hardy travelers know, getting sidetracked can be an adventure, even in a climate-controlled world. I retraced my steps and landed at the Roy Thomson Hall. The Toronto Symphony Orchestra was performing a Chinese New Year's special that afternoon, and when I poked my head into the street-level lobby, I could hear music being piped in from the main stage. I didn't have a ticket, but the lobby and music store were open and free. So I ordered a drink from the lobby bar, plopped down in a seat overlooking the snowy cityscape and listened to conductor Sam Wong turn the Year of the Pig into a mellifluous celebration.

When the music stopped, the black-tied attendants prepared for the exodus. From my perch, I watched the concertgoers jostle to get out the front door, fumbling with coats and kids. I calmly finished my drink, then slipped past the crowd on my descent downward.

My serendipitous foray added a much-needed boost to my step -- stairs, ramps and too many food-court squares can be exhausting on the legs -- as I now ventured to the far end of the PATH map, the bus station.

To reach the terminal, I crossed through a surprising range of architecture. I rode the escalator to the Santiago Calatrava-designed Allen Lambert Galleria at BCE Place, where soaring white arches cut the blue sky into puzzle pieces. I detoured through an underground parking lot (follow the Squirrel signs; if you hit Moose, you're too far left) to take a self-guided tour of City Hall, which includes contemporary artworks and a peek at the mayor's office. I passed through Atrium on the Bay, an open-plan department store where I bounced on the display beds. In Eaton Centre, an ersatz Pentagon Mall, I watched Canada's species of mall rats, nearly indistinguishable from ours. Finally, I reached my end point.

I was about ready to turn around and thread my way back when I caught sight of the next departure: Montreal. Hey, Montreal has an underground city, too. If only the buses departed from below . . . .

* * *

Nighttime in the PATH is often a quiet affair: maybe cocktails at Canoe, which overlooks Lake Ontario and its islands, followed by a $32 truffle burger at ByMark and a nightcap and sports highlights at the Duke of Devon. Unless the Maple Leafs are in town. Then the scene is pure raucous, painted in blue and white.

Since I was in a hockey town in a hockey country, I figured I should join the fray. The Saturday game at the Air Canada Centre was a biggie: the 40th anniversary of Toronto's last Stanley Cup win and the 80th anniversary of their first game. I started scouring the doorways and corridors for scalpers.

"Anybody selling hockey tickets, selling, selling, selling?" called out a pasty, rodent-faced man standing outside the arena entrance, half-shielded by a concrete column.

"Are there scalpers here?" I asked.

"No, just me," he said, scanning the crowd as they filed inside. "This is my office."

"So," I asked, "are you buying or selling?"

"Both. They're going for a thousand bucks each," he retorted, before slinking off.

Even in Canadian dollars, so not worth it.

Inside, the enormous arena was a mash of fans moving en masse toward the gate, but near the ticket windows, a handful of people were politely queuing up. They were waiting to see if any last-minute tickets would be released. I asked a guy standing behind me about the likelihood of this happening. He said it was pretty slim, but I could buy a ticket from scalpers outside. I don't mind the cold of the rink, but the freeze of the city? Pass.

In the end, however, I did get game. In the center's play zone, which is free and open to the public, I went face to face with a cardboard goalie. I smacked those pucks hard -- and scored one. Not bad for an American.

* * *

Living underground can eventually take its toll on your psyche. And skin complexion. On Day 2 as a mole, I started to crave sky and open spaces and even a slight sting on my cheeks. I was feeling wan, and I needed altitude. According to the map, the CN Tower is reachable by skywalk, and at 1,815 feet, I could certainly get my height fix.

This is the part where I have to admit a small defeat. The skywalk unfortunately ended a few yards from the CN Tower's front door. I had to descend a short hill outside, but, I rationalized, it was like fetching the morning paper at the end of the driveway in your bathrobe. A quick out, then back in.

I raced down the lane and, before I could see my breath, I was inside one of the world's tallest towers. After 42 hours below street level, I wanted to go as high as possible. The elevator took 58 seconds to reach the first level, then another couple of seconds to the 1,465-foot Sky Pod. The black sky was flecked with snow and the world below was frozen hard. There were no snow angels here, just ice, gray and hard edges.

I circled the observation deck, finally seeing the topside of the city I'd been crawling beneath for two days. The deck soon became cold, and I craved the protection of the underground. I quickly pressed the down button and returned to the warm depths of Toronto.