Reading my Mom's Rotary Club of Briarcliff Manor blog, I saw mention of "Parallel Universes." It really isn't so mystical for those of us who know Edwin A. Abbott's Flatland - a wonderful little book that I read in grade school that helped me understand the unimaginable. For those more visually than literally inclined, there's now a charming movie version available on DVD (it's in my collection).
I recall getting headaches in my youth trying to think of what additional dimensions we might be living in (beyond our 3 space and 1 time dimension). Now physicists have theorized that we exist in 11 dimensions (string theory). Having mulled about Flatland for so many years, I have some inkling about the mysteries they are unveiling. It's quite fun now to think a bit about the possibilities of what it means to be part of a universe of additional dimensions outside our experience. And I don't get headaches thinking about it anymore.