Invisible platform
From Tardis Wiki, the free Doctor Who reference
The Seventh Doctor stands on top of a series of invisible platforms over London. (GAME: Dalek Attack)
By 2254, a series of invisible platforms were present over London and Paris. They could become visible upon being walked over, and the London platforms appeared as blue ovals with white cores surrounded by a faint yellow glow, while the Paris platforms appeared as slightly less rounded yellow ovals, grey around their edges, and also with white cores. (GAME: Dalek Attack)
