Venus de Brizet
France
The Venus de Brizet is a marble sculpture of Venus (Aphrodite to the Greeks), discovered in a field in Saint-Just-sur-Loire, in Loire, France), in 1937. Originally thought to be an ancient Roman work, it was classified as a historical monument (monument historique) in 1938, before it was revealed that it was actually sculpted in 1936 and buried the same year by an artist who imagined the hoax for advertising purposes.
Data from Wikidata (CC0). Summary from Wikipedia (CC BY-SA).