My "hidden gem" recommendation for Torres del Paine is the Mirador Ferrier trail, which was suggested to me by my hotel's activity concierge. This  relatively short but steep hike starts near the Lago Grey hotel and provides 700 meters of elevation gain.   It wasn't a very popular area; I only saw a couple other people on the trail, compared to the hundreds on the Mirador Torres hike. The view from the Ferrier mirador is spectacular -- possibly the most impressive vista I've seen anywhere in the world: Pinnacle, pinnacle, pinnacle. Glacier, glacier, glacier. Lake, lake, lake,..., each a slightly different shade of blue. Easily worth the pain I caused my knees by rushing up and down a little too quickly.

I spent three days in Torres del Paine in November of 2017. Regretfully, my schedule didn't leave me quite enough time to do the W trek, but I experienced some wonderful day hikes.  The highlight was the hike to the Torres Mirador, a challenging 19 km trek. I was by myself, but there are lots of people hiking, so it's pretty easy to fall in with a group going your same pace for some camaraderie.  I was well-rewarded for the effort with some spectacular views of the Torres at the small lake that's at their base.  On other days I also did smaller hikes such as to the Mirador Cuernos which passes the very nice Salto Grande waterfalls and visited Lago Grey for the very worthwhile boat trip to view the Grey Glacier.  

Logistics

I stayed at the Rio Serrano Hotel, which is right on the southern border of the park, with fabulous views into the park and a nice place to stay very comfortably that I would recommend highly. I got a rental car in Puerto Natales, where I stayed overnight one night before and after my park visit to line up with the bus schedules to & from Punta Arenas airport. I enjoyed having the freedom of the car since it let me cover a lot of territory across the park. Puerto Natales isn't a bad little town, but my hostel completely failed to live up to its good reviews. Early November was a great time to visit -- I experienced great hiking weather. The park was busy, but I wouldn't call it overcrowded and you could find nice spots to enjoy some solitude..

 

I had a slightly different experience than other reviewers here, so I thought I would add my perspective with a medium length stay in the area without doing the W trek.