The Yonaguni Monument , also known as "Yonaguni (Island) Submarine Ruins" , is a submerged rock formation off the coast of Yonaguni, the southernmost of the Ryukyu Islands, in Japan. It lies approximately 100 kilometres east of Taiwan.

Mu is a lost continent introduced by Augustus Le Plongeon (1825–1908), who identified the "Land of Mu" with Atlantis. The name was subsequently identified with the hypothetical land of Lemuria by James Churchward (1851–1936), who asserted that it was located in the Pacific Ocean before its destruction. The place of Mu in both pseudoscience and fantasy fiction is discussed in detail in Lost Continents by L. Sprague de Camp.