Before the Panama Canal, every ship crossing between the Atlantic and Pacific had to round South America, and there were only three ways through. The Strait of Magellan ran north, sheltered but winding. The Drake Passage ran south, open ocean and infamous for storms that swallow vessels whole. Between them lay the Beagle Channel - narrow, only five kilometers wide at its tightest, walled by mountains that drop glaciers straight into the sea. It is navigable by large ships, though sailors generally prefer the alternatives. The channel runs east to west, splitting near its Pacific end around Gordon Island into two branches, a watery fork at the edge of the map.

Two settlements face each other across the channel, and they are about as far south as people permanently live. On the northern Argentine shore sits Ushuaia, which calls itself the end of the world and has the souvenirs to prove it. On the southern Chilean side, smaller and quieter, lies Puerto Williams. The waters between them teem with life that exists almost nowhere else. Peale's dolphin, endemic to Patagonia, breaks the surface alongside dusky and Commerson's dolphins. Magellanic penguins crowd the rocks. Andean condors ride the updrafts overhead, while sea lions haul out on islets the locals simply call La Isla de los Lobos - the island of wolves.

For most of the twentieth century, the three small islands at the channel's eastern mouth - Picton, Lennox, and Nueva - poisoned relations between Chile and Argentina. The Beagle conflict simmered for decades and nearly boiled over in December 1978, when Argentina launched Operation Soberanía to seize the disputed islands by force. The invasion fleet was hours from landing. What stopped it was not an army but a telegram: Pope John Paul II, alarmed, dispatched a personal envoy and offered to mediate. Argentina, overwhelmingly Catholic, turned its ships around. Six years of papal negotiation followed before the Treaty of Peace and Friendship, signed in 1984, confirmed the islands as Chilean and ended one of the Cold War's quietest near-catastrophes.

Long before the Beagle ever sailed these waters, the Yámana people lived along the channel and its tributaries, settling sites like Bahía Wulaia roughly ten thousand years ago. They had their own name for this place - Onašaga - and their own account of how it came to be. In a Selk'nam myth, the channels and lakes of Tierra del Fuego were torn open where slingshot stones fell to earth during the hero Taiyín's battle with a witch who had hoarded the waters and the food of the world. Sail the channel today past the Romanche Glacier or the Les Éclaireurs lighthouse near Ushuaia - the one tourists call the End of the World - and Darwin's beryl blue is still there, exactly as he saw it.

Near the channel's western reaches, a stretch the cruise crews call Glacier Alley delivers the scenery Darwin struggled to describe. Tidewater glaciers spill down from the Darwin Icefield one after another, several named for European nations - Italia, Francia, Alemania, Holanda, España - their ice walls glowing the same impossible blue against the dead white of the snowfields above. Meltwater thunders into the channel; the air turns sharp and cold. Below the surface, the water is unusually rich in life, which is why this is one of the best places on the planet to watch rare dolphins. It is a hard landscape and a generous one at once - punishing to live in, overwhelming to look at, and almost entirely unchanged since a seasick young naturalist first reached for the words to capture it.