Not being able to find the sloths is the joy of the Montreal Biodome. It is not quite a zoo, not quite an aquarium, not quite a botanical garden, but more than all three combined. The idea is to try to create entire mini-ecosystems, each with its own regenerating flora and fauna. And to devise a way for more than a million tourists a year to see it without destroying it.
The Biodome opened in 1992, on the site of the old velodrome at the Olympic complex in the east end of Montreal. It was a unique and ambitious project. The oval building was divided into four self-contained quadrants, each representing a different ecosystem: tropical forest, Laurentian forest, St Lawrence marine ecosystem, and the polar regions.
The Montreal zoo and aquarium were closed down and some of the animals were transferred over to the new facilities. The Montreal Botanical Gardens, one of the best regarded in the world - and conveniently, right across the street - helped find appropriate plants.
The result is astonishing. The first zone you enter is the Tropical Forest. Hidden in its 2,500 square metres of damp heat and lush foliage are thousands of animals, from monkeys to alligators. As you walk along the raised walkway, parrots swoop by overhead and turtles bob in the stream below. The longer you stand still and the harder you look, the more you can spot. There are piranhas and anacondas and other teen-pleasers, as well as my elusive favourites, the sloths.
The next quadrant contains the lake, river and granite mountainside of the Laurentian Forest. The real Laurentian Forest is about an hour's drive north of Montreal, but the Biodome's version has the added bonus of neat turns - such as a video-camera in the beaver lodge so that you can see Canada's national animal relaxing after a long day of gnawing.
The temperature in the Laurentian Forest changes with the seasons, mimicking nature's cycles. In the autumn, the leaves change colour. In the winter, it gets cold enough for the animals to hibernate and the plants to lie dormant. In the spring, life starts to pick up speed and by the summer, the otters, lynx and more than a hundred other mammals and birds are busy doing what comes naturally - most of which is quite noisy.
Next comes a real tour de force: the St Lawrence marine ecosystem. The St Lawrence river links the Great Lakes to the Atlantic. It surrounds the island of Montreal but its murky grey waters don't tend to inspire Darwinian flights of naturalist discovery. Until you see it from below.
At the heart of the ecosystem is a giant aquarium, made to look like the shoreline to the St Lawrence, filled with 2.5m litres of salt water. From above, you can see kittiwakes nesting on mock cliffs at the water's edge, and ducks lazily paddling on the surface.
From below, it is a whole other world. Deceptively colourless, the hundreds of fish from the St Lawrence look as if they have enough character to inspire a Dickens novel. Brute-like sturgeon patrol the basin while skittish crabs scuttle along the bottom. Halibut float by, looking improbable, and schools of cod and mackerel swish around rather like a swarm of confused bees.
But the best part comes when the ducks decide it's time to eat. One by one they dive, head first, feet desperately motoring them down, down, down. The effort is palpable. Once on the bottom, they nudge the rocks with their beaks, trying to dislodge small bites. Finally, lungs busting, they realise it's time to surface. They point their heads up, and stop paddling. Whoosh, like mini-torpedoes, they rocket to the surface, using their feet as rudders to avoid whacking into circling bass. It looks ridiculous fun.
From there, you proceed to the last zone, the guaranteed crowd-pleaser: the Polar World. The sub-arctic area has puffins and guillemots, but what everyone really wants to see are the four species of penguins.
This is the only climate zone you can't walk though. Not surprisingly, since the temperature can get down to 2C. Rather, you sit on amphitheatre- style benches and watch the penguins though a wall of plate glass. Well, there ain't nothing cuter than a cavorting penguin. What more can you say? The Biodome knows that, and visitors always leave with a smile on their face.
I, however, was not smiling when I left. I had hunted my missing sloth while fantasising about casually passing the naturalist and saying: "yeah, you know that sloth you've been looking for? He's just over there, behind that capybara. I don't know how you managed to miss him."
Oh well. I guess I'm just going to have to go back and try again.
The Biodome is located next to the unmissable Olympic Stadium (it looks like an improbably enormous, Seventies version of a spaceship). Technically, the Biodome is at 4777 Pierre-De Coubertin Avenue, but no one that you ask has ever heard of that street. The best way to get there is to take the metro to Viau, which is a 15-20-minute ride from down-town. While in the area, it is well worth visiting the extensive Botanical Gardens across the road, as well as the quirky Insectarium. Free shuttle buses run between all the attractions. Entrance to the Biodome costs $9.50 (pounds 3.95) for adults, $7 (pounds 2.95) for concessions, $4.75 (pounds 2) for kids 6- 17, and it is free for children under five.
For more information about the Biodome, call 00 1 514 868-3000. Or check out the website: www.ville. montreal.qc.ca/biodome
There are two non-stop jumbos each day between Heathrow and Montreal, on Air Canada (0990 247226) and British Airways (0345 222111) - the latter operating also on behalf of Canadian Airlines. Additionally there are charters, mainly from Gatwick, operated by companies such as Bluebird Express (0990 320000). Fares are around pounds 250-pounds 300.
In September crews on Air Canada went on strike, grounding the airline. The Independent is receiving a number of criticisms of the way passengers were treated during and after the flight, such as this from Kim Reynolds:
"My 10-hour direct outward flight to Vancouver turned into a 12-hour flight to Los Angeles, a five-hour stopover and a three-hour flight to Vancouver. I therefore arrived half a day late and absolutely exhausted. Trying to reconfirm my return flight during my stay, I spent eight hours on the phone trying to speak to a human being at Air Canada. When I did get through, I was told that the problem was because the airline was having a seat sale to regain customers after the strike! What about the passengers trying to complete a journey with you? I have not had so much as an apology from Air Canada. I've been treated better in the past by Aeroflot."
Visit Canada Centre, 62-65 Trafalgar Square, London WC2N 5DY (telephone 0891 715000, a premium-rate number).