One of the distinctive features of Japan's public utilities is the wide variety of manhole cover art. The phenomenon is not strictly limited to "manholes" designed to allow humans to enter subterranean conduits; it can also be found on the panels covering Japanese fire hydrants (as pictured here), which are usually under the surface of the street. The link above offers a gallery of over 200 examples of Japanese art over holes in the ground, some quite brightly colored, like this one from Nikko; others rather dull but still locally distinctive, like this one with porpoises from Chichijima in the Ogasawara (aka Bonin) Islands north of Iwo Jima.
Of course, Japan isn't the only country that indulges in manhole cover art. Take at look at the Russian gallery entitled Sewers of the World, Unite! or the utility cover artist Bobby Mastrangelo at The Grate Works.