The Cerro Guanaco Trail is the most difficult trail of the Tierre del Fuego. But it will reward you with the most beautiful view.
When I went there I had planned to take the bus at 10 am, but I just missed it. So I took the 11 o’clock bus to the park. Until I was at the visitor center and registered, it was 12. The last bus leaves at 7. I’ve asked if there was enough time left. They told me yes, you need about 6h, even if the map says 8h. Anyway, if you have a sunny day, I would recommend to take the earlier bus to have more time. So you could also spent some time just to relax at the lake.
First you walk about 30min flat and along the lake. At the beginning you follow the Hito hiking trail, which leads to the border to Chile. Then there will be a branch to follow the Guanaco Trail. There is a sign, telling duration will be about 4h one way, do not start after 12:00. I had just registered for the trail, so of course I continued even if it was after 12.
The path will go first through the forest for 1h uphill until you reach a viewpoint. Then it flattens a bit and you go further through the forest. Then through a mystic forest with many curves trees, very nice. Afterwards you reach a big muddy field. Sooner or later you will do a step where the bottom is not hard enough and you stand in the mud. From here you can already see the summit. However, it is still 2km on a stony path, steeply along the mountain. The gusts of wind can partly be so strong that you might think it will blow you down. After another hour you will reach the summit at a height of 973m.
The ascent took me 2.5h (3h from the visitor center). The summit rewards with a great view all around. You can see the park, a big lake, Ushuaia from above and you can see the whole Beagle Channel. So it is really worth it. I stayed for 30-45min before I went down again.
Overall and with the break the Cerro Guanaco Trail took me around 6 hours. At the visitors center is also a restaurant so you can have a drink if you need to wait for your bus