Added to the conventional FPS control keys are two extra keys that move the player in ana and kata direction in 4d space. If you go in this extra direction the space around you changes, the room transforms.

[H]e called into presence the kazees and the witnesses, and brought in the three Qurundeels, and brought in the first damsel, and her own sister who had been ensorceled, and he married the three to the three Qurundeels, who had informed him that they were kings, […]

The ghost flights, defined as those with no passengers or less than 10% of passenger capacity, operated from all 32 airports listed in the data.

to overlook a valley from a hill