Northwest of Punta Arenas and Puerto Natales, the Torres del Paine National Park is located on a section of the Patagonian steepe and is the most popular park in Chile. Mountain biking is permitted on many trails. For a great starter ride, try the 12 mile singletrack along Grey River running east-west in the park.
To reach Torres del Paine National Park, plan to use inter-country airline, LAN Airlines, to fly from Santiago to Punta Arenas. Rent a car from Turismo Southland (011-56-61-241-143). Then drive 155 miles north to Puerto Natales. Then another 90 miles northwest to the park. Note, there may be bus service available from Punta Arenas to Puerto Natales.
Overall, Grey River is the 4th most popular mountain bike trail of all 4 mountain biking rides in Chile.