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Designed by Skidmore, Owings & Merrill in 1974, the former Sears Tower was the world's tallest building until 1996. The 110-story, 1,730-foot-tall structure may have lost its title and even changed its name, but it’s still tough to top the Willis Tower's 103rd-floor Skydeck—on a clear day it offers views of Illinois, Michigan, Wisconsin, and Indiana. Enter on Jackson Boulevard to take the ear-popping ride up. Check the visibility ratings at the security desk before you decide to ascend.Video monitors turn the 70-second elevator ride into a thrilling trip. Interactive exhibits inside the observatory bring Chicago's dreamers, schemers, architects, musicians, and sports stars to life; and computer kiosks in six languages help international travelers key into Chicago hot spots. For many visitors, though, the highlight (literally) is stepping out on the Ledge, a glass box that extends 4.3 feet from the building, making you feel as if you're suspended 1,353 feet in the air. Before leaving the tower, check out Calder's spiraling mobile sculpture The Universe in the ground-floor lobby on the Wacker Drive side.