10 Dollars

Redonda is an uninhabited volcanic rock in the Caribbean — roughly 1.6 square kilometres — that has never had a functioning government, population, or economy. Its "kingdom" is a literary fiction dating to the 1880s, when Matthew Dowdy Shiell claimed it for his son; the title passed through a succession of writers and eccentrics, most notably the novelist M.P. Shiel and later Jon Wynne-Tyson. Coins issued under its name are fantasy pieces with no monetary function whatsoever, produced entirely for the collector market.