Laputa

Laputa was a floating island above Venice, Italy. In 1609, Irving Braxiatel held a gathering of aliens on Laputa in order to create the Armageddon Convention. When he first heard the name, the First Doctor was confused — Laputa was the name of a fictional island in Jonathan Swift's Gulliver's Travels. (PROSE: The Empire of Glass)

In the far future, Professor George Litefoot compared the Venusian floating city Amtor to Laputa. (AUDIO: Voyage to Venus)

Behind the scenes
The name is one of Jonathan Swift's jokes; la puta is Spanish for "the whore".