Mataderos is where the locals hang out on a Sunday; filled with homemade produce, young gauchos and parillas to do die for. It's only a short distance out of Buenos Aires capital but you feel like you're miles away. A perfect day out if you're looking for something a bit more authentic and unique.
There are many markets such as the ones in Recoleta and San Telmo that are worth going to but if you're wanting to avoid the hoards of tourists and experience the real side of the city then this is the place to come to.
Come with an empty belly. Leave before it gets dark so you're not left stranded as it can get a bit sketchy at night.