Mar del Plata
Come summer, Argentina becomes obsessed with Mar del Plata. The city of 600,000 residents is the country's most popular beach resort—and at least five times as big as any runners-up. Dull gray sand and chilly water may not make for the best beach experience, but in Mar del Plata activities like people-watching, eating, shopping, and clubbing are just as important. The sands are comically crowded in January and February, when there's a carnival-like atmosphere day and night.
The tourist infrastructure hums, with more than 700 hotels and countless eateries. Off-season can get a bit lonely, though the windy sands and almost deserted boulevards feel cinematic. The city becomes literally cinematic each November, when it hosts the Festival de Cine de Mar del Plata, Argentina's biggest film festival.
Although most hotels are within walking distance of a beach, and the city center is navigable on foot, you'll need a taxi or bus to get to other parts of town, like the port. There are several downtown-area beaches; the summertime action revolves around Playa Bristol. The trendiest strip of sand is south of the lighthouse, but you need a car to get here comfortably.