"now I'm thinking of Debussy's Sunken Cathedral"

This prelude, La Cathédrale Engloutie by Claude Debussy, is also known as The Engulfed Cathedral or The Drowned Cathedral

Listen on Spotify: La Cathédrale Engloutie

It is based on the legend of the city of Ys in Brittany, drowned beneath the sea through the treachery of the King's daughter, Dahut. It is said that one can still hear the church bells ringing beneath the waves.

                   

This sonnet by Ian Grose captures the myth and the prelude together beautifully:

Par-Ys Debussy's piano speaks of a silence / More quiet than air: a city sinks at night. / The breath of buildings finally exhaled; / The highest tower catches the last light. /For Ys, whose submerged walls are weak with weight, / I wonder if it would be a disgrace / To see its name become a syllable; / It's beauty borrowed by another place. / The borrower, not knowing what it took, / (It's tower swimming still in light and air) / Is subject to the rule that things will end / (All the more transient, all the more fair) / Suggesting that its fate will be the same: / The price of beauty built into its name.