A beach is so much more than a sunny stretch of sand—although there are plenty of those, too, in Brazil, Argentina, and Uruguay, where Hanya Yanagihara surveyed more than 9,000 miles of coast to come up with 13 of the continent's best strands. Here, on South America's east coast, you'll find not only tropical heat (and the hardbodies who come with it) but pebbled shores populated with penguins, unpeopled stretches where palm trees are your only company, and waves without end that attract fledgling and serious surfers alike. Call it the thinking man's beach guide—to mindless pleasures, to be sure, but also to much, much more.

BRAZIL
Praia de Sibaúma, Natal
Good For: Scenery / Sun
Natal, the capital of Rio Grande do Norte State, is famous for its beaches, but Sibaúma, 90 minutes south of the city, is in a league of its own. The strand is bracketed by twin tidal pools (in the morning, when the water is low, you can watch white-and-yellow crabs scuttle into their rocky pockets), and the continuous one- to two-foot waves are perfect for bodyboarding. What's most striking about Sibaúma, however, is its absences: no garbage (just handfuls of green and burgundy seaweed tossed up by the sea), no tourists (just a few patient fishermen, thigh-deep out past the tide pools), and almost no development, in deference to an adjacent turtle sanctuary (just a solitary inn at the top of the cliff that backs the beach). This is not a typical tropical-fantasy beach: There's little shade, and the storm-colored water, while clean and nearly as warm as the air, is made silty in parts by the ceaseless surf. But one can believe, walking along its solidly packed sand, that it is wholly one's own—a fantasy of a different sort.
The 411: The five-suite Kilombo Villas & Spa—a well-intentioned but unrefined property with glorious views of Sibaúma—is a three-minute walk away, although staying here means near-complete dependence on its adequate but expensive restaurant (55-84-3246-5534; kilombovillas.com; doubles, $350—$483; entrées, $9—$30). Alternatively, Tocada Coruja Pousada, with a resident bird sanctuary and one of the area's most popular restaurants, is a short car ride away in Pipa, a pretty little village with some nice beaches of its own (55-84-3246-2226; tocadacoruja.com.br; doubles, $128—$379; entrées, $9-$21).
When to go: Bodyboarders will prefer the winter months of June, July, and August, but locals recommend late February and March, when the weather is warm but not sultry, the waves are manageable, and the post-Carnaval hangover means that everything moves in pleasant slow motion.

Praia dos Nativos, Trancoso
Good For: Sports / Sun
Sure, some of its most committed admirers now helicopter in from Rio de Janeiro and São Paulo for a long weekend, but at its heart beautiful Trancoso, in Bahia State, remains a hippie town. There are the requisite bikini shops and open-air Thai restaurants, but here the storefronts are painted vivid shades of mint green and acid pink that complement, rather than compete with, the shaggy flame trees and clumps of pink-and-yellow ginger that surround them. At the end of the Quadrado, or town square, the lawn of the sixteenth-century Church of St. John gives way to a glorious overlook of the area's seven miles of beach. The main, two-mile Praia dos Nativos begins where the Rio Trancoso flows into the sea, and is speckled with cafés blasting Bob Marley remixes and with beachgoers of all ages. Just 15 minutes to the north, however, is Taipé—a tawny plain fringed with mangrove and coconut trees that is all yours: no sunbathers, no swimmers, and no noise save for the gentle surf. At times, the water is swimming pool flat, and so cool and sparkling that it's like gliding through soda pop.
The 411: Etnia Pousada—a fantasy of a tropical B&B, with eight bungalows, a pool, and a rustic-chic outdoor restaurant—is a pleasant 20-minute stroll inland (55-73-3668-1137; etniabrasil.com.br; doubles, $243—$304; entrées, $13—$18). If you'd rather be bang on the beach, Pousada Estrela d'Água is a cozy, crisply run resort with two pools (55-73-3668-1030; estreladagua.com.br; doubles, $455—$877). Among the Quadrado's more notable restaurants are O Cacau, with its riffs on traditional seafood dishes (55-73-3668-1266; entrées, $17—$29), and Maritaka, a swinging beer-and-pizza joint (388 Rua do Telegrafo; 55-73-3668-1702; entrées, $15—$30).
When to go: The best people-watching, weather, and water are from Christmas through Easter.