This is some tidbits taken from the site I posted before, but I thought their discussion on the island was fascinating. Both of these are regarding the unbelievable acid algae island.
"It's the fulcrum in the story, where the realistic becomes the surrealistic. This illustrates the point that, similar to religion, each story has believable and unbelievable elmements. And if we are to accept a story, we must believe all of it, or none of it. This ties in with faith and the suspension of disbelief with respect to the miraculous elements of religion."
"Just an example, take the chapter of the floating island, which was also of much interest to our book club. This story is fascinating but, as this discussion shows, literally incredible to some. But if we view it as part of a fable or symbolic universe, then the island is a sort of metaphor: an apparently safe place where our tiger selves (that is, our fierce, instinctual, physical selves) would stay forever, well satiated, if our other rational or spiritual selves didn't recognize the dangers and force it to leave. I think most people have been on such islands: places where they feel safe and sheltered but which slowly, inevitably eat away at them, causing them to become lesser individuals, with no more stature than tamed, doomed meerkats."