Quite often in fantasy books the author will include a song / poem at the beginning or between chapters in order to set the scene / provide atmosphere, or even foreshadow things to come. Sometimes these songs or poems can be effective, and other times they can seem like just a bit of added fluff. Either way, they at least succeed in letting the author’s imagination take a break from structure and run a little wild, as imaginations should.
Think about a world or characters you have created—either from an already published piece or a Work In Progress. Take a break from prose for a moment, and bring the context of your story into a more poetical perspective. Look at your worlds and characters as if they are heroes from a long-forgotten past, and write a song or a poem about them. Remind your readers who they are and what they stand for / what they’ve accomplished. Let yourself get reacquainted with these people and places as well, and see them from a different perspective. Let the music of the language add a different tone to your creation, and find some way to weave that music and that feeling into your prose once you return to it.