This piece is based on an ancient Breton myth in which an entire city is submerged underwater off the coast of the Island of Ys. The cathedral of the city 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.
 
The use of open fifths at the beginning allude to the idea of church bells that sound from the distance. The cathedral gently emerges from the water; the music includes important narrative instructions (Peu à peu sortant de la brume - Emerging from the fog little by little). Then, after a section marked Augmentez progressivement (Slowly growing), the cathedral has emerged and the grand organ is heard at a dynamic level of fortissimo. This is the loudest and most profound part of the piece, and is described in the score as Sonore sans dureté (sonorous without harshness). Following the grand entrance and exit of the organ, the cathedral sinks back down into the ocean and the organ is heard once more, but from underwater. Finally, the cathedral is gone from sight, and only the bells are heard, at a distant pianissimo. (source: Wikipedia)