Architecture buffs on a pilgrimage bow down to the Monadnock, two buildings in one that depict a crucial juncture in skyscraper development. The north half is the older, traditional design from 1891 (with thick brick walls and a plain facade), while the south is the newer, mod half (with a steel frame that allows for jazzier-looking walls and bigger windows). See the difference?
Monadnock Building
Chicago