Why to Go: Feria de San Telmo, the antique market that opens every Sunday in one of Buenos Aires' most charming neighborhoods, has been in continuous operation for decades and draws in a mostly local crowd of bargain hunters. The selection is generally exceptional, and vendors do a great job restoring and cleaning their goods so they absolutely sparkle. It's a terrible place to shop if you're looking for one particular object, but amazing if you're browsing and willing to be flexible.
What to Buy: There are always a lot of metallic kerosene lanterns for sale. Whether that's because the electrical grid in the city used to be unreliable or because Argentineans love a flame is entirely unclear, but they make great lamps if you're ready to take the time to wire them.