"Underground theater"

First blog review of The Other Side by Ted Green, dating from the previews:

It's an intense little show about war -- between countries and between parents and their children. Harris gives an amazing performance as a Mother who has been waiting for the return of her son for over twenty years.
...
The audience today seemed like a real New York crowd. I'm guessing most of the audience were subscribers to the theater. I liked the show, but I heard a lot of discontented muttering on the way out. In fact, when the show was over several seemed unsure if the show was actually over or if it was simply an intermission.