Chicagoland's Yorktown Center

The 25 million dollar YORKTOWN CENTER was dedicated in October 1968. At that time, the gigantic complex was the second-largest enclosed mall east of the Mississippi (Greater New York City's ROOSEVELT FIELD MALL being the largest).
Photo from the DuPage County Historical Museum 

A full-page newspaper ad announces the grand opening of the YORKTOWN super mall. Take note of the thermometer depicted on the right. This 25-foot-high instrument stood in the Grand Court. It was calibrated to register a constant 72 degrees year-round.
Advert from Long-Pehrson Associates