Start where the road ends. Drop Montevideo in the rearview mirror, even though the capital of Uruguay has the vibe (and steakhouses) of Buenos Aires 25 years ago. Get lunch in Punta del Este, the Malibu of South America, and drive on. Skip lovely José Ignacio, a really south Hampton, where the rich practice simplicity. Just east of there, at the Laguna Garzón, the coast road stops and skips a beat before you land in Cabo Polonio.

Sputter over the mouth of a lagoon onto a two-car ferry. On your right will be a beach with a mile-and-a-half-long left break; on your left, an eco-resort your girlfriend will melt over. Keep moving, if you can, to the sandy point. You've entered Rocha, a different South America, where the beaches get wider, the life slower, and a Brazilian vibe kicks in.

Off the grid but increasingly on the map, Cabo Polonio was founded by fishermen, squatters, dropouts, and hippies, but sits inside a national park, with no road access, electricity, or running water. Ditch your rental car at the trailhead and ride in a huge, balloon-tired truck over the dunes and out to the beach, where there are a couple of small hotels, though most people rent a bed in one of the 400 ranchitos, tiny two-room houses that dot the bluffs. Walk miles of empty beach, learn to surf among sea lions, or shop – there's one store, with no ice. Read or write by candlelight. You might see right whales, or just sit still for hours hoping to. Pay no attention to the locals, who tend to wander the streetless village with a smile, often burning a joint. There are other towns out here, but Cabo Polonio is where you need to be now.

The government is slated to break up this bohemia and will remove at least 100 illegal houses soon. "We may not be here when you come back," says Laura Cánepa, who owns the Posada de los Corvinos, a small pink house that is, with seven beds, one of the largest guest accommodations in the area. Working from photographs, park rangers demolish any new additions or improvements to the rustic houses. The settlement's future is in doubt, but time changes everything. Cánepa doesn't miss the days before cell phones. "Now I text my neighbor right in front," she laughs. Her new LCD lights drain the solar panels less, and life is beautifully bearable in this half-unplugged township of the imagination. Someday electricity will arrive. Maybe they'll even put a bridge over the lagoon. But for now, you've reached the end of your road.

More information: Fly to Montevideo and take a five-hour bus ride ($15), or land in Buenos Aires and ferry to Montevideo. The funky, solar-powered Posada de los Corvinos sits a few hundred yards from the sea (from $10).