Designed by renowned architect I. M. Pei, L.A.'s most distinctive skyscraper (it's the round one) is the tallest building between Chicago and Singapore. Built in 1989 at a cost of $450 million, the 76-story monolith is both square and rectangular, rising from its 5th Street base in a series of overlapping spirals and cubes. The Bunker Hill Steps wrapping around the west side of the building were inspired by Rome's Spanish Steps. "Gee whiz" fact: The glass crown at the top -- illuminated at night -- is the highest building helipad in the world.