back to that pleasure-dome:

I don't know how common this interpretation is, but my teacher last year explained it as a metaphor for artistic success. Xanadu, an idyllic, imaginative world, is Kubla Kahn's success--the domain he created. It relates to Coleridge's desire to be as successful as Wordsworth, to create his own pleasure dome, an artisitc legacy. There are many terms that relate to art, music or imagination: "damsel with a dulcimer", "symphony and song", "music loud and long" and "that dome in air."

Some hard rock type band made a song called Xanadu that relates to this interpretation.

But I guess it could just be about sex . . .