Ponta do Calcanhar lies just outside the fishing town of Touros, near the northern end of the great curve of Cape São Roque — the northeastern shoulder of South America. The Portuguese name for the point is a joke about anatomy: calcanhar means heel. Ships coming up from the south and ships bearing in off the Atlantic both have to round this heel, and there is a reason the Brazilian Navy chose to mark it so emphatically. About seven kilometres offshore lies a coral reef. The light exists to keep vessels off it. Locals also use a grander name, Esquina do Continente, the Corner of the Continent, and with a chart open in front of you it is hard to call that an exaggeration.

The tower is a tapered cylinder, stiffened along its length by four vertical ribs and painted in broad horizontal bands of black and white so that it reads as clearly by day as it does by night. At 62 metres — 203 feet — it is the tallest lighthouse in Brazil, one of the tallest concrete lighthouses anywhere in the world, and the nineteenth tallest of the world's traditional lighthouses. Because it stands on rising ground rather than at the water's edge, its focal plane sits higher still, 74 metres above the sea. The character is a single white flash every ten seconds. In clear air that flash carries thirty-eight nautical miles, roughly seventy kilometres, far enough that a ship still below the horizon can pick it up and know precisely which corner of the continent it is coming around.

There has been a light on this point since 1912, when the original tower went up in cast iron under the name Olhos d'Água, standing 50 metres tall. Cast iron and Atlantic salt make poor long-term companions, and a second cast-iron tower, 52 metres tall, replaced it in 1937. It was the concrete tower standing today - begun in 1941 and built tall enough to throw its beam well out over the reef - that finally solved the problem; its lamp was first lit in 1943. The lighthouse still answers to several names depending on which chart, which agency and which generation of local you happen to consult: Calcanhar, Touros, and the old Olhos d'Água.

Unlike most working lights, this one lets visitors in. The tower opens to the public every morning from nine until eleven, and the climb is a spiral staircase of 277 steps to an observation platform, with a further twenty-one-rung ladder for anyone permitted to reach the lantern itself. From the platform the geography that a chart only implies becomes obvious — dunes, coconut palms, the long white line of surf breaking over the offshore reef, and the coast plainly bending away to the west. This is not a ruin or a museum piece. Single-storey keeper's houses stand at the tower's foot, and the station still has a resident keeper.

Touros itself is a small place: fishing boats hauled up on the sand, wind turbines turning on the ridges inland, a scattering of pousadas. The water off it is not small at all. Traffic moving between the Caribbean, Europe, West Africa and the ports of northern Brazil all rounds this heel. On a clear night the beam sweeps out over that shipping every ten seconds, the same interval hour after hour, marking the exact spot where a continent changes its mind about which way to face.