The High King by Lloyd Alexander (The Chronicles of Prydain, Book Five)
The final book in Alexander’s Prydain series. Elegant storytelling steeped in Welsh mythology. What strikes me the most is how elegiac and melancholy it is, from the various sacrifices that each main character has to make, to the bittersweet ending. And it’s all the better because of it. It affected me as an adult; I can only imagine how it would’ve affected me had I read it as a kid.