Terror on the 103rd floor: Chicago's Sears Tower plans to open a glass-bottom Skydeck in June. Visitors to the 4-foot "Ledge" walkway will step into glass enclosures that extend 4.3 feet beyond the building. Beneath their feet in dizzyness-inducing splendor will be Chicago, 103 stories below, with an inch and a half of glass between person and pavement. Woo-whee!