The user might have meant "Palace Theatre" or "Movie Palace" as a generic term for historic theaters. The keyword includes "free exclusive", so perhaps a promotion where you can watch Harry Potter movies for free at a movie palace.
So, how do you unlock this achievement? Finding a screening is the hardest part, as most major movie palace events require a ticket purchase. However, "exclusive" doesn't always mean by-invitation-only; often, it means a unique experience that is separate from regular showings. Here's where to look for the magic. movie palace harry potter free exclusive