You don't really notice it unless you go looking for it. Mostly, it's hidden away underground, catching the eye at street level only in places where its irrational exuberance breaks through: as a funky glass-tiled box at Akabanebashi, say, or huge, alien-looking metal leaf shapes at Iidabashi. Even the lucky commuters who descend into its depths every day often give the impression of thinking they are merely on a train -- nodding off or reading the paper or staring blankly at their shoes.

Wake up, sleepyheads! Tokyo's Oedo Line, brand-new in December, isn't just a way to get to and from work. Mind you, it's not surprising that people mistake it for an ordinary subway line. It has all the trappings: trains, tracks, ticket machines, entrance gates, signs, maps, toilets and uniformed men waving lanterns. But it is so many other things besides: the city's best-kept entertainment secret, a magical mystery tour, a string of surprises, a mood enhancer, a giant underground loop of hands-on art galleries that cost next to nothing to visit.

It all depends on how you look at it -- or even if you look at it, which admittedly is hard to do when you're in a bleary-eyed rush. Form and function blend so seamlessly on the Oedo Line that it's easy to overlook the one while you're busy counting on the other to get you to work on time. (Though you would think even a blind man might notice the difference transferring from boring, grimy Hamamatsucho Station to the Oedo Line's Daimon Station next door, as glamorous as a "Star Trek" set with its severe gray tiles, silver pillars and clever, recessed red lighting. There's a zing in the very air at Daimon.)