1. Why don't we go to a movie?

Question

(In this sentence, does 'movie' mean 'movie theater' or 'motion picture'?

2. Why don't we go to the movies?
(In this sentence, does 'movies' mean 'movie theaters' or 'motion pictures'?)

Answer 1

#1 would be clearer if you wrote "Why don't we go see a movie?" (meaning a particular motion picture, film, or movie)

#2 could mean either to the theater or to see motion pictures, probably whatever's showing!