Glass floors require the trading of architectural intuition for faith in the invisible as structural. They heighten the awareness of standing above something; the refraction of glass, conveying a jewel-like preciousness; its reflections, momentary glimpses of solidity. In many in situ archaeological sites, glass floors reveal the gaps between body, weight, and archaeological feature; an awareness of the destructive power of gravity threatening the object of archaeology below. Standing on this “solid” air conveys supernatural levitation, but, at height, can also instil a disconcerting and visceral fear because the floor cannot be seen. The article examines architectural instances of glass, specifically in sites of art, tourism, and archaeology, and predominantly in floors, which suspend occupants above, or at least confuse the relationships between floor, feet, and standing. It is particularly interested in the difficulties of assuming that glass provides an uncomplicated visual relationship between viewers and in situ archaeology.