In the mid-19th century, intrepid explorers began to shine a light on the darkness of the deep. The mystique of what lay beneath the surface of the vast oceans inspired awe in aquarium enthusiasts, Decadent artists, and authors, including Jules Verne and Hans Christian Andersen. Ever since, books, films and visual arts have invited us to contemplate the sea as both the wellspring of all life and a resolutely alien world. "Wonders - A Literary History of the Deep Sea" recalls the era of undersea telegraph cables and the heyday of the aquarium. It presents mermaids, octopuses and jellyfish and explores some of the many works of art that conceptualise undersea marvels or dream of vanishing ecstatically into the depths, into this other element. It is the story of how we imagine life was formed underwater and on our planet. It is about the historical basis for our modern perception of the sea and a call to action before the fantastic creatures with whom we have only just begun to become acquainted disappear forever. Frits Andersen is a professor of Comparative Literature at Aarhus University. His previous works include "The South Sea Island. A Geography of Pleasure" (2023), about islands, archipelagos and the sea.