Mather Tower

Mather Tower (later Lincoln Tower, as designated on the Michigan–Wacker Historic District roster; now identified primarily by its address) is a Neo-Gothic, terra cotta-clad high-rise structure in Chicago, Illinois, United States. It is located at 75 East Wacker Drive in the downtown "loop" area, adjacent to the Chicago River. The 521-foot (159 m)-high building is sometimes called "The Inverted Spyglass" by Chicagoans due to its highly unusual design, an 18-story octagonal tower atop a more conventional 24-story rectangular "box." Briefly the tallest building in Chicago at the time of its completion in 1928, it remains the city's most slender high-rise structure at only 100 by 65 feet (30 by 20 m) at its base. Its needle-like form was encouraged by the 1923 Chicago Zoning Ordinance, which called for "setback" buildings. The interior space within the upper octagonal spire contains the least square footage per floor of any Chicago skyscraper.

Building data from Wikidata (CC0); heights normalised. Summary from Wikipedia (CC BY-SA).