I certainly believe that what we perceive as humans is just the tip of the iceberg. I don't necessarily believe in vampires or werewolves or that kind of thing, but I believe there is definitely a realm we don't necessarily have access to.
The trick to being a novelist is to act like an iceberg. Make it seem as if you're displaying only one-tenth of what you know, and the other nine-tenths isn't visible and never mind if that part is pure styrofoam!