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. 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)
