Hiking the French Valley is part of the W-trek through Patagonia's Torres del Paine National Park. It's about 16 mi round-trip from Refugio Paine Grande to the French Valley Mirador, to see the French Glacier and the Paine Massif as close as you can get. The trail is diverse and only reaches a steep height at the last 5.5 km on the way there. You begin at Lago Pehoe and take grassy paths through the forested valley, on an terrain that the locals call "Patagonia flat," i.e. an undulating up and down of several feet. On the way you'll see tiny magenta--and edible--berries that taste just like apples; you'll cross small glacial streams where you can fill up your water bottle with fresh, wild water. You'll trek right by the Cuernos, or the "Horns," another well-known set of peaks in Torres del Paine. Over the French River you go as you get deeper into the valley, over wobbly rope bridges.
The final 5.5 km to the French Valley Mirador has you balancing on thousands of loose boulders on your way up. The very top of the trek feels like being in the middle of a Patagonian fishbowl: Paine Massif to your left, French Glacier in front, the Aleta de Tiburon (the Shark's Fin) and the Cuernos to the right, and turquoise Lago Pehoe behind you. The weather up there turns freezing since you're so close to the glacier, so make sure to wear all your layers once you stop. The whole trek takes about 10 hours with a group. On the way back, be prepared for crazy weather patterns as you go in between the mountain passes in the afternoon; it can turn windy, rainy, cold, then sunny all in the same hour.