Torres del Paine are located in National Park TdP, at 4 hours hiking from TdP campground. The acces path starts from Laguna Amagra National Park Service Hut, situated at 120 km north from Puerto Natales.
You have to be there early in the morning because the towers walls have east side orientation. You have to start hikking a day earlier to be able to camp at the nearest point you are aloud: Campamento Torres. Next day you have to hike for 1,5 hours from camp site to Torres del Paine