Follow the main trail from Laguna Capri, which continues gently to Río Blanco, base camp for the Cerro Fitz Roy experience. From here it's a very steep climb to Laguna de los Tres (four hours one way). Bring loads of water and supplies - it's a toughie. But the extraordinary close view of Cerro Fitz Roy, as well as the eerily still glacial lake itself, make the effort worthwhile.
Be prepared for high, potentially hazardous winds and allow time for contemplation and recovery. Then scurry down 200m to the left of the lookout for an exceptional view of the emerald green Laguna Sucia.