La Cathédrale engloutie (The Submerged Cathedral) is a prelude written by the French composer Claude Debussy for solo piano. It was published in 1910 as the tenth prelude in Debussy’s first of two volumes of twelve piano preludes each. It is characteristic of Debussy in its form, harmony, and content. The piece is based on an ancient Breton myth in which a cathedral, submerged underwater off the coast of the Island of Ys, rises up from the sea on clear mornings when the water is transparent. Sounds can be heard of priests chanting, bells chiming, and the organ playing, from across the sea.