Hi-yi-yi (or Hi-Iay) was a fictitious small archipelago in the Pacific Ocean supposedly destroyed by the secret nuclear test of the US military in the 1950s. It was created by Gerolf Steiner, a zoology professor at the University of Heidelberg, to be the habitat of his equally fictitious Rhinogradentia.
The tropical archipelago measured some 1,690 km2 (650 sq mi), and the highest peak (2230 m or 7316 feet) was on the main island, Hiddudify (Hy-dud-dye-fee). The islands were
Each island was home to a distinctive fauna, dominated by many species of Rhinogradentia or Snouters – the only mammals in the archipelago, besides humans.
Hiddudify was inhabited by the Huacha-Hatchis. The first description of the archipelago published in Europe was provided by Swedish explorer Einar Pettersson-Skämtkvist, who arrived in Hiddudify in 1941, after escaping from a Japanese prisoner of war camp. In the late 1950s, as a consequence of atomic bomb testing, the islands suddenly sank into the ocean, destroying all traces of the snouters.