MISSING CEILING TILES: A few ceiling tiles can be taken out. Lights can be inputted above and triggered by proximity? or maybe by pressure sensor mats on the ground? Lights can glow brighter and change color. Maybe even flicker when standing under them? Tiles can be taken out to form shapes? Tiles = pixels?

DOORS TO NOWHERE: Projections of humorous/startling actions can be projected?

FLOOR STRINGS: Projections of strings can be on the floor. Using computer vision, strings can move according to the movement of people's feet. Strings can get tangled around feet? change color? ripple? be plucked and make sound? Possibly even respond to sounds, vibrations?