Constitución 40, Loc 57
Backstage Experience is an always-hopping food and music venue in Patio Bellavista, a couple of blocks from the Baquedano Metro in a free-standing mid to upscale foodcourt and shopping area, where middle class and upper-middle class Chileans often come for an after-work drink, and where you'll hear at least six languages being spoken on any given day.
The restaurant and music venue itself is well-situated, has an enormous seating area, brings good bands in from out of town and locally, and serves a variety of food from cheese and meat platters to pizza and sushi. The food is fair, and some say the pizza passes muster on the international front, though the crust is very thin, so despite how large they are, you might want one for yourself.
It's a good place to spend an evening, grab some nibbles, people watch, and maybe catch some good music. See website for details of who's playing on any given night.