From the bridge over the Blanco River along Provincial Route 23, take the trail that goes alongside the river.  After approximately two hours, you will reach an overlook with a westerly view of the Piedras Blancas Glacier.  You cannot cross the river here. Continue to the Poincenot Camp and from there; head back to El Chaltén or camp overnight.  
Another alternative is to take the trail from El Chaltén to the De los Tres Lagoon and cross the footbridge over the Blanco River. After crossing the footbridge, at the mountaineering camp, detour right, heading down river. Continue on this path to the Piedras Blancas Stream, descending west, a little less than an hour's walk from Camp Poincenot. Turn 90° west, in front of the glacier, on the trail that traces the right bank of the stream. Cross, just before the river’s start. Once on the other side of the river, follow it down, almost to the lake, where you will have an excellent view of the northeast face of Fitz Roy and its glacier.