I strongly recommend the horseback riding at Lago Roca. The guy responsible for the horse ridings is Luciano Cuenca, you can take a look at his website here http://cabalgatasdelglaciar.com/. There you will find all the horse ridings he offers. I did only the Lago Roca that takes only one day, so I'll write about only this one.
Luciano picked me up in my hotel at 9AM and drove me, my wife and 3 other persons to his Estancia (farm), about 40min from El Calafate, where there he prepared the horses while we waited, talked and enjoyed our mate tea and the beautiful scenery of Patagonia. His Estancia is in a beautiful place located inside the Los Glaciares National Park (where is also the famous Perito Moreno glaciar).
We rode the horses inside the Park enjoying a calm ride and the landscape. He took us up a hill where we had an incredible sight of the Perito Moreno glaciar, the mountains, the river, lake Roca and the mountains. After that we rode more until the shore of a river where Luciano prepared the meal for us. Everyone ate the good argentinian chorizo. For me and my wife, we had a delicious vegetarian meal prepared by Luciano too (you must tell Luciano before if you have any food restriction).
After the Lunch we headed back to the Estancia around 3PM. Luciano then drove everyone back at their hotels.
This is a MUST do if you are in Calafate. Luciano is a nice guy who loves what he does. The ride will give you a feel of the true patagonian spirit. This is not a mass touristic activity as the Perito Moreno minitrekking, so you can enjoy more peacefully the Patagonia.
Cheers and bon voyage,