Torres del Paine is undoubtedly the most famous trek in Chile, due to a combination of spectacular scenery, highly-developed infrastructure, and effective marketing.  There are two ways to do the trek: you can either hike a nine-day loop around the entire park, or you can do just the more accesible portion of the circuit, known as "the W" due to its shape.

We had decent weather on the first day of the trek, so we did a side trip to catch the Torres ("towers" for those whose Spanish is even worse than mine) themselves before the clouds rolled in.  Didn't quite make it.