This is a story about Underground Los Angeles. Not the underground music scene -- the underground art scene. The subway art scene.Yes, there is a subway in L.A. Even some Angelenos don't know about it, and most have never used it. But a system of subways and light rail was started in the early 1990s, and it's steadily expanding.Depending on where you live, the subway's an efficient way to get downtown, which has become more of a destination in recent years, what with the Music Center with its plays, concerts, ballets and operas; fine museums; a funky, lively boho arts district; the Frank Gehry-designed Disney Concert Hall; the relatively new Cathedral of Our Lady of the Angels. Plus the old attractions: Chinatown, Little Tokyo, Olvera Street's cheesy but charming Mexican street fair, and such architectural gems as Union Station and the Bradbury Building, featured in "Blade Runner."