You’ve done it! You made it to level 20! Your characters is at the apex of their power. Feats taken, spells learned, items collected.
The DMG offers a few options for other rewards. Notable among them is Epic Boons, which provide a benefit for accumulating experience points beyond what you need to reach 20th level. If you play for an extended period of time at this level, they’re a great way to continue letters characters advance.