What structures do stand behind the expression the movies (we're going to the movies)? It confuses me that it is plural (movies) and with the definite article (the). It seems that in the same way you say the woods (we went camping in the woods).
The movies entered the language very early, before World War I, at a time when your ticket entitled you to see a large number of works lasting only a few minutes each.
And even when works got longer, the multiple bill persisted. Well into my childhood in the 1950s and 60s, what you expected to see when you went to "the movies" was several pieces: two or three trailers for coming attractions, a "short subject" of five or ten minutes, a newsreel (but these were being superseded by TV news), and one or two cartoons before you got to the "feature" film.
The multiple bill has mostly vanished today, but the phrase lingers.
The movies is an idiomatic expression to say the cinema or cinema.
Let's go to the movies.
I've always wanted to work in the movies.
Woods means "an area of trees, smaller than a forest."
Let's take a walk in the woods.
You cannot generalize and say that "the [plural word]" is always and idiomatic expression.