One end of the giant " Goodyear AIRDOCK Hangar in Akron, OH. The massive doors are over 22 stories in height. According to Wikipedia - At each end of the building are huge semi-spherical doors that each weigh 600 tons (544 000 kg). At the top, the doors are fastened by hollow forged pins 17 inches (43 cm) in diameter and six feet (1.83 m) long. The doors roll on forty wheels on specially-designed curved railroad tracks, powered by an individual power plant each, which can open the doors in about 5 minutes.
More info about the Airdock can be found at en.wikipedia.org/wiki/Goodyear_Airdock