“The 1990 changes to the endowment were made after much prayer in the Upper Room of the temple.
“There is no special upper room, or, any ‘special’ rooms certainly aren’t in the upper parts of the [Salt Lake] temple.
“Many years ago, a ward friend of mine, who worked in the temple as a full-time church employee, gave me a tour of the place. We went everywhere, even up to the roof. The uppermost room is an attic used for storage. The next down is the assembly room. Former missionaries who had the Salt Lake mission home and accompanying temple experience have been there. The next floor down is dog-leg shaped to accommodate the two floor high nature of the Celestial room. Also, the Holy of Holies, whose entrance is in the Celestial Room, is two floors tall. On this dog-legged floor are the Quorum of the Twelve, Seventies, and Elders rooms. Those last rooms, as I remember it, served as locker rooms for general authorities. There were lockers with name plates on them, kind of like an NBA locker room. There was also a dining room where the 12 have a meal after their Thursday quorum meeting. We wandered around on other floors first because the 12 were still having lunch on the day of my little tour.
“The next floor down has the Telestial, Terrestrial, and Celestial Rooms, along with the sealing offices and sealing rooms. This level is the ground floor; when you’re seated in the Telestial Room, you are facing west.
“Below that is the first basement–Creation Room, Garden Room, and baptistery. There is a second basement below that–a maintenance area with access to the foundation.”
~Tom Krause, Facebook Post, 19 October 2015.