It was one of the most memorable places I have ever visited. I am studying abroad semester, and the first place I look into visiting again was Mount St. Michel. What a journey through history. My wife and I just got back from our first trip to France. If you're going to France put this on the list of sites.
Pictures do no justice.
It's about 3 hrs from Paris and the D-Day Beaches are close by. You can also go to St. Malo to spend the night. Well worth the time and energy. I can't wait to take my children there once they are old enough to begin to appreciate it. This castle is one to be seen in the evening, as well as a day stop, because of the magical appearance the castle takes when lit up.