Invigorated and cosseted, Simon Calder found instant karma in the city that never sleeps; Tokyo
By five o'clock on the last morning of your stay, you face a difficult task. Not to convince yourself that the Japanese capital is the most exciting city on earth, since by now you can imagine few rivals for the title. No: the trick required at the moment is to persuade your drooping eyelids to remain open just a little bit longer. If you can stay awake, you will witness the finest piece of theatrical commerce anywhere in the world.

When BBC2's Travel Show was looking for a city to feature as the ultimate long weekend in the last programme of its 1996 series, the answer lay 6,000 miles away across Siberia. If you leave on Friday night, you can boast that you have "been there, done that" and be back at your desk by Tuesday morning.

You could easily to avoid ever going to Tokyo by merely reciting the traveller's mantra: "Ooh - Japan is far too expensive." But compared with, say, Paris and New York, the world's busiest city is a place for the frugal.

This much, you will discover in due course. For the moment, you need to seek out some calm from the controlled frenzy of the average Tokyo afternoon. So you check in to a place you had selected from the small truckload of tourist information that the Japanese National Tourist Organisation in London provides. Welcome to the ryokan.

If you have never previously somewhere that provides instant karma rather than instant coffee, now's your chance. Ryokans are small, traditional Japanese hotels that have endured despite the headlong westernisation elsewhere in the city. Imagine living inside a kite, enlarged (but not very much) into a big, paper-walled box where the floor is a neat array of tatami mats - raffia with attitude. At the centre, a delicate collusion of china tea cups is orchestrated into warm, wet action by someone who is neither a chambermaid nor a geisha. If all you want after a long flight is a nice cup of tea . . . well, they don't come any nicer.

Invigoration is on hand in the shape of the ryokan's communal bath. Scrub yourself scrupulously clean first, then slide gingerly into the sublime, steaming pool. Around now a new anxiety may manifest itself: the fact that the bureau de change at the airport gave you only 160 yen for each puny pound. My friend Jeremy had informed me before I set off, "You know they charge pounds 20 for a hamburger out there, don't you?" Jeremy is right about most things, but in fact McDonald's sells a bacon-cheeseburger for 90 pence. So there.

The secret of Tokyo is to trust the city to make life easy. Your ryokan is probably in the Ikebukuro area of Tokyo: inexpensive, Bohemian, like a cleaned-up, high-rise version of Camden Town. "Ikky", as you will soon be calling it, is a stop on the Yamanote Line. This is a supremely efficient rail loop that stops almost everywhere of interest; if you can't get there on the Yamanote line, you're probably better off not going.

By Day Two, your body-clock should be getting in step with the pace of the city. Forget about ticking off the sights; the grounds of the Imperial Palace are pretty dull anyway. Instead, go shopping. Japan may be the world's economic powerhouse, but even in Mitsukoshi - Tokyo's Harrods - commerce is tempered with ceremony. Precisely turned-out women, in lemon yellow from toes to bows, address the waiting crowd outside the doors at exactly five to 10, so that 300 seconds later the monumental doors can swing open.

The impecunious head straight for the food hall in the basement, where in a whirl of free tastings you can indulge all your culinary fantasies: 27 different (and delicious) things to do with tofu; the taste and texture of rough and raw sugar; preserved grasshopper, whose legs will all fall off in your mouth.

Then, to an ordinary office block, built in the 1960s for a modest enterprise called Sony. The company still has its spiritual home here,where it shrugs off the Sixties, and this Millennium, and embraces the next. These seven floors are the eighth wonder of the world.

By now it is five on Monday morning. If you had wanted commercial theatre, then London or New York should be your destination. But for theatrical commerciality, you have to be at the Tokyo fish market. The tastiest tuna are poked about, bought and sold by an audience hungry for sushi, in a chorus of yells and screams. Within an hour the creatures are on their way to the sushi bars of Tokyo, where the mechanised conveyor belts will usher their flesh into a flotilla of seafood, joining scallops and salmon, squid and octopus to feed the 25 million citizens. Within four hours you will be flying home, with perhaps just a litre of duty-free sake as evidence of the greatest adventure in the East.