The Cincinnati Bengals spent their first three seasons at Nippert Stadium (1968-1970).
Today, for your viewing pleasure, is the NFL Films' 1968 season review of the expansion AFL Bengals. This video includes many excellent glimpses of Nippert Stadium in its 1954-1991 configuration, which seated 28,000. When the Bengals played at Nippert Stadium, they had the smallest seating capacity in professional football.
The current configuration of Nippert Stadium includes the upper deck on the east sideline, the video scoreboards, and the club seats, press box, and lodges added in this most recent round of renovations, all of which are missing in this video.