The Maracot Deep (sub-titled: The Lost World Under the Sea) is a short novel written by Arthur Conan Doyle first published in The Strand Magazine from october 1927 to february 1928, then continued as The Lord of the Dark Face in april and may 1929.

In april 1927, Conan Doyle wrote in a letter that the story would be called "The Fabricius Deep" but was renamed before publishing.