The star destination of Chilean Patagonia is called Torres del Paine. This Park, accessible from the town of Puerto Natales (interesting city tucked away in a beautiful setting), is an ode to lovers of hiking and adventure. Mountains, valleys, lakes, glaciers, wild and pure rivers from these gigantic and blue blocks of ice, forests, open meadows... All that awaits you in an environment in which the main characters are the peaks of Torres del Paine. In terms of fauna, there are many birds (eagles and condors among them), and guanacos are the easiest to see among mammals. But if you are lucky you might also see armadillos, foxes, huemules (Southern Andean deer) and even pumas. The Park can be visited with a guided day tour (even from El Calafate, Argentina), but this is expensive and it is not the same. The backpacker can go on their own perfectly (by hitchhiking or by bus from Puerto Natales to the entrance) and get into that Patagonian nature by hiking one of the two most popular circuits: the “O” or the “W”.
Differences between circuits:
W: Shorter (80 km) and less vertical (3000 m vertical drop in total), it takes about 4 days on average.
O: Longer (130 km) and more uneven (6000 m vertical drop in total), it takes about 8 days on average.
The W is actually part of the O. I did not do the O, but from what I have heard/read it is worth doing the whole thing, and it is not necessary experience or being super fit. In the O, the variety of landscapes will be even greater, and you will be more time in contact with that wild and incredible nature. The main disadvantage is that you will have to carry more weight (food and clothes). The W is awesome anyways, perfect for those who have no so much time and/or feel like a four-day hiking in the woods is more than enough for them.
Throughout the Park there are campsites (and shelters/hostels for those without a tent). Some campsites are free (at least back in March 2014), so if your budget is tight try to organize your route to camp in those free of charge. What you will not get rid of is the cost of the ticket (entrance to the Park), which is quite expensive (21000 Chilean pesos; 6000 for nationals). Along the way you will also find a couple of hostels/restaurants where they serve food and hot drinks to recover your energies and forget a little about the packet soups.
As for the best time to visit, according to the weather it would be between December and February, but in those dates it is also overcrowded. Maybe the perfect moment is the beginning of March (April is already very cold). Two final tips. 1) Try to carry only the essentials, leaving the rest of the luggage in a hostel in Puerto Natales. 2) To leave the Park in the W (in the O you return to the starting point) there is a stretch of about 15 additional km that you can do on foot instead of taking the boat (very expensive).