When I was a kid I remember seeing this animated movie but I can't remember the name...

When I was a kid I remember seeing this animated movie but I can't remember the name. I've tried searching for things I remember about the film but I can never find the movie. Maybe you guys can help?

Here's what I remember:

>Kids are in some sort of castle or fancy place
>Kids find a large set of doors and are told to keep away
>Kids find key and open doors
>Kids wuss out and decide not to go in
>Kids close doors but forget to lock them
>Some sort of monster escapes since doors were unlocked

Can't remember much else. I saw the movie probably mid 90's. Might have been an anime but not sure. Any ideas?

Little Nemo?

prolly not it but pagemaster?

...

He said 90s.

ONE FLEW OVER THE CUCKS NEST?

The smurfs?

Little Nemo?

Check "Little Nemo Adventures in Slumberland"

Pet Semetary