Location. You'll find Enchanted Tales with Belle in the New Fantasyland part of the park, right next to Be Our Guest (with the Beast's castle looming in the distance). If you're walking into the area from behind Cinderella Castle, you'll see Belle's cottage on your left, right across from Seven Dwarfs Mine Train.
It was presumably given to the Beast by the Enchantress as his only window to the outside world. It is unknown if it has always been enchanted, or if it was originally an ordinary mirror owned by the prince that became imbued with magic by the Enchantress along with the castle.
When sunlight or other bright light shines onto the mirror, the mirror appears to become transparent. If that light is reflected from the mirror onto a wall, the pattern on the back of the mirror is then projected onto the wall.
Relive the magic of Disney's Beauty and the Beast during an unforgettable reenactment starring Belle, Lumiere... and you! Explore Maurice's cottage and workshop—home to mementos and gadgets—before being magically transported to the Beast's library.