What is the most hauntingly beautiful part of your world's lore?

What is the most hauntingly beautiful piece of lore from your world? What's something from your worlds that is happy, but just a little sad?

In Alria, certain people living on the floating islands of High Celestia can hear a very faint singing at dawn and dusk. Only a select, magically-inclined few can hear this singing. It only happens at sunrise and sunset, and can only be heard in rural parts of High Celestia. It sounds like an angelic choir, regarded as the most beautiful singing you'll ever hear, but you'll never see where it's coming from.

The angelic singing actually comes the Celestial Guardians: great, feathered dragons that protect the world and cleanse the land of cursed evils. They are normally invisible to the average person, but anyone who's been to the Aetheric Plane can see them. At dawn and dusk, the Guardians sing a magical song that blesses the world and keeps their people safe. Only those who have seen the Guardians can hear their sacred singing. So if you ever hear any mysterious singing coming from the sky, that's the angels wishing you a good morning and good night.

The world canonically has a theme song, and it's an angelic prayer that wishes you well.