Dark Waters (Once Upon a Time) is to take Snow's heart. The Land of Untold Stories is revealed to be the Mysterious Island from the book as the same name. The "Nautilus" is based on the submarine from "Twenty Thousand Leagues Under the Sea". Captain Nemo based on the protagonist from Jules Verne's novel "Twenty Thousand Leagues Under the Sea". Hook refers to the giant squid that attacks him as a kraken. The kraken is a legendary sea monster of giant size that is said to dwell off the coasts of Norway and Greenland. The episode posted its lowest numbers so far in the series, as
Twenty Thousand Leagues Under the Sea the book from the initial concept is a portrait of Tadeusz Kościuszko, a Polish national hero, leader of the uprising against Russia in 1794, with an inscription in Latin: "Finis Poloniae!" ("The end of Poland!"). Margaret Drabble argues that "Twenty Thousand Leagues Under the Sea" anticipated the ecology movement and shaped the French avant-garde. Theodore L. Thomas in 1961 said that "there is not a single bit of valid speculation" in the novel and that "none of its predictions has come true". He described the depictions of the diving gear, scenes, and the "Nautilus" as "pretty bad, behind the times