La Piojera is an expression of popular chilean culture. Foreigners usually like it for being quaint. The place is realy dirty (the tables, the wall, the floor, everything). You should drink "terremoto", made of a mix of a low quality wine, fernet and pineapple icecream (even though there are other places with better terremoto, but this bar is famous for this drink). I recomend you to eat something for having a better service, otherwise they don't even care of getting you a table. The place is very crowded, and is located in a popular sector of the city, so you must be REALLY cautious with your belongings, even more if you're easily recognizable as a foreigner.
Even though my opinion of La Piojera doesn't sound really good, it's a must-see, you will enjoy a different experience for sure.
This review is the subjective opinion of a TripAdvisor member and not of TripAdvisor LLC.