Which American animated film depicts a girl who finds an idealized parallel world behind a secret door?

Neil Gaiman is my favorite living author.

Globular Martian, Its human imagination so don’t be surprised that some may show similarities along the story lines. Remember there is only one Populated world we can prove exsists. !!!

Globular Martian, my first thought, but not an option

MC Merci, In the UK many years ago there was a kids programme called The Lion, The Witch and The Wardrobe. It was based on The Chronicles of Narnia. Sounds like a familiar theme.