Dull, bleak, gray and cheerless are a few of the words that could describe Tokyo's architectural landscape. Glaring neon aside, it is a city seriously lacking in color.

It's ironic, then, that one of the most imaginative and colorful public art projects in the metropolis can be found in the bowels of the city, along the length of the Oedo Subway Line.

As soon as you descend into any one of its 26 stations, it becomes obvious that this is no run-of-the-mill railway line. Not only does each station feature unique designs that reflect the historical and/or cultural characteristics of the area it serves, but they also host a diverse array of fascinating art installations. Located at depths of between 30 and 40 meters, the Oedo Line must count as one of the world's deepest public art spaces -- at least geologically. Makoto Ishimura of the Tokyo Metropolitan Subway Construction Co., which oversaw the 10-year-long Oedo project, describes it as "a kind of giant theme park, inside of which is an underground art gallery."