From Puerto Natales, take the bus or hire a driver to take you the Paine National Park. Once in the Park, it is necessary to either drive or, if the road is flooded ( quite possible in late spring ), hike ( after getting a park guard to ferry you via boat ) to the Estancia Cerro Paine. From here a trail leads first south, then west up the Rio Ascencio valley to the base camp used by the Italians in 1963 during their first ascent of the South Tower. From here continue up the valley thru a forest of linga trees around to the west side of the Towers.
This is the original route on the South Tower climbed by the Italians in 1963. First ascent by J. Aiazzi, A. Aste, C. Casati, N. Nusdeo and V. Taldo, Feb. 9th, 1963. It is about 22 pitches and can be climbed in two days with good weather. The pitches are rated 5.3, 5.6, 5.7, 5.7 A1, 5.6 A1, 5.6, about 1485 feet of 5.0, 5.6, 5.6, 5.7, 5.7, 5.6 A1, 5.6, 5.7, 5.7 and 5.7. A mostly free route.
See The American Alpine Journal - 1994, pages 10 - 19 for more information.
Note - I cannot speak from personal experience regarding this climb but I would recommend 2 sets each Friends and wired stoppers and a small selection of pitons from some Bugaboos / blades to 1" angles. 200' ropes would be helpful. Crampons and ice axes may be needed. As for any climb in Patagonia, warm stormproof clothing, and bivy gear for emergencys are essencial.
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