This one is so obvious I'm surprised I haven't thought of this before. Even the name of the piece fits!
"
In the Hall of the Mountain King" by Grieg, aka Bilbo inside Erebor. Can you hear his careful footsteps, his heart racing, and in the end his flight back to the Dwarves?
I know that both Tolkien and Grieg were inspired by Scandinavic mythologies, but that's as far as my knowledge goes. I've never studied those mythologies. Maybe someone more learned than myself can make some connection that would link Grieg's and Tolkien's "halls of the mountain king"?