South of Puerto Montt, the population thins and the vegetation thickens. This is the region of northwest Patagonia commonly called the "Carretera Austral," named for the dirt route that runs south to tiny Villa O'Higgins between 48° and 49° latitude. It's a 1,240km (769-mile) dirt-and-gravel road that bends and twists through thick virgin rainforest, past glacial-fed rivers and aquamarine lakes; jagged, white-capped peaks that rise above open valleys; and precipitous cliffs with cascading ribbons of waterfalls at every turn. If you like your scenery remote and rugged, this is the place for you. Though much less traveled than the famous Torres del Paine, in many ways, a journey down this "highway" is the quintessential Chilean road trip, and many of its natural attractions are as stunning as any you'll find farther south. There are also some of the country's best fly-fishing lodges, one of the world's top rivers for rafting, hot springs, and a sailing journey to one of Chile's most awe-inspiring glaciers. It is also home to fjords that are ideal for kayaking, and the rainforest jungle of Pumalín Park, which was severely affected by the May 2008 earthquake that wiped out the village of Chaitén.

The Carretera Austral runs from Puerto Montt in the north to Villa O'Higgins in the south, and passes through two regions: the southern portion of the Región de Los Lagos and the Región de Aysén, whose capital, Coyhaique, holds almost half the sparse population of the region, home to less than one person per square kilometer.

The area largely straddles the Andes, unlike most of Chile, where the range's summits form the eastern border.

A first few roads appeared in the 1930s, but before the mid-1970s, much of the area could only be reached by ferry or plane, and trucks servicing its tiny villages and fishing hamlets mostly had to enter from Argentina.

Worried about a very real threat of war with Argentina in the 1970s, then-dictator Augusto Pinochet sought to fortify Chile's presence in this isolated region by connecting the existing roads with the rest of the country. More than 30 years later and at a staggering cost above $300 million (and counting) and the lives of more than two dozen men, work continues.