Sir Gawain and the Green Knight by an anonymous late 14th Century author is a chivalric romance written in Middle English. But you don’t have to be proficient in Middle English to read it as there are several excellent translations available, including some on line.
This is a delightful Medieval poem about the adventures of Sir Gawain, King Arthur’s nephew. The events occur during two consecutive Christmas seasons and involve a jolly green giant, a beheading, a quest, a journey into the wilderness, a magic castle, a beautiful lady, a couple of delightful seduction scenes, a ruse, an unexpected twist, and probably the biggest oops blunder in English literature.
The poet gently exposes the foibles of human nature and the difficulty of living up to courtly ideals with their concomitant code of chivalry. And he does so with sympathy and humor neatly gift wrapped in eloquent diction to celebrate the season.