From Puerto Bahía Túnel on Lago Viedma south of El Chaltén , the park’s best lake excursion is the catamaran Viedma Discovery’s voyage to Viedma Glacier. The full-day trip includes ice-climbing on the glacier, which is Argentina’s largest even though its lakeside face is small.
Sailing from Bahía Túnel, the ship rounds the irreverently named Cabo de Hornos (Cape Horn) to enter an iceberg-cluttered area before anchoring in a rocky cove. After disembarking, visitors hike to an overlook of the glacier and 2,677-meter Cerro Huemul; those who wish can strap on crampons for a 1.5-hour trek on the ice (even some pretty sedentary Porteños do so).
Well-versed in glaciology, the bilingual guides provide more personalized service than the Fernández Campbell excursion from Puerto Bandera. While the price does not include lunch, they do provide an aperitif on the glacial rocks.
Departure time from El Chaltén  is 8:30 a.m., while the boat sails from Bahía Túnel at 9 a.m. (US$50 pp plus US$6.50 for transportation from El Chaltén for those who need it). For details, contact Viedma Discovery (Güemes s/n, tel. 02962/493110).
Formerly just a restaurant, Bahía Túnel (tel. 02962/493043, bahiatunel [at] hotmail [dot] com, US$50 d) has opened two guest rooms that share a bath. The restaurant is still a good breakfast choice, with picture-window views across the lake, and also serves lunch, afternoon tea, and especially the sunset dinner.