Whether you get there by water or via dry land, arriving at Argentino Lake in Patagonia is always one of the highlights of a trip to Argentina.
The main thing to do at this lake is spend the day out on its icy blue waters in a boat. Visitors have two options available to them: head for the Upsala Glacier to the north, or head for the Perito Moreno Glacier to the south. The whole national park is a UNESCO World Heritage Site, and arriving at the foot of either of these immense masses of ice by boat is a simply magical experience.
You can also go on a nice walk along the shores of the lake from Calafate. It's a very enjoyable hike to do, and I got to see lots of wild birds when I did it. I advise you to dress warmly however: not only is the beach exposed to the wind, it's positively gusty.