Vehicle Assembly Building, Kennedy Space Centre, Florida
Each of those doors is the height of a complete Saturn 5 plus launch tractor. The shuttle stack only needs two leaves to be opened. For scale purposes, look at the gantries just in front of the doors on the bottom left. A small white dot can be seen - this is the shirt of a worker on the gantry. The brown-grey building on the left of the VAB is one of the shuttle hangars, used whilst the Shuttles are being reconditioned for their next flight.