Building Q was a building related to the Nonary Game. It was supposed to be a complete copy of the Gigantic, but it was located in the middle of the Nevada Desert. The reason it is known as "Building Q" is presumably because the exit door is Door q.
Building Q's interior was built as a copy of the Gigantic's. Due to this, the puzzles were exactly the same. Just like the Gigantic, Building Q had multiple decks connected by a Central Staircase.
D Deck held the 3rd Class Cabin, and was flooded at the beginning of the Nonary Game.
First Nonary Game
Building Q was used by Cradle Pharmaceutical and Free the Soul for the First Nonary Game to put the kids who excelled at transmitting through the morphogenetic field in there to transmit the answers to the puzzles to the kids in the Gigantic. Clover Field and Ennea Kashiwabara were in Building Q.
Due to a mix up regarding Akane Kurashiki, Akane was sent to the Gigantic instead of Building Q. To fill in Akane's missing role, there were two sisters in Building Q.
Nine Hours, Nine Persons, Nine Doors
Building Q was later used by Crash Keys for the Second Nonary Game, as the Gigantic had been sunk in the previous Nonary Game. Its presence was only made known after the players of the game had escaped, as they had previously assumed they were on a ship because D Deck had been flooded.