On the eastern Andean slopes, Parque Nacional Los Glaciares comprises over 750,000 hectares where slowly flowing ice gives birth to clear frigid rivers and vast lakes interspersed with Magellanic forests, along the Chilean border west and north of El Calafate .
A UNESCO World Heritage Site, it’s famous for the Moreno Glacier , which draws thousands of sedentary visitors for day trips but also pulls in scientists absorbed in glaciology and climate studies.
In general, the park’s southerly sector, west of El Calafate, gets day visitors for passive sightseeing. The northerly sector—a 3.5-hour bus trip from El Calafate—attracts those seeking to spend several days in vigorous exercise, either trekking or the far more demanding and dangerous technical climbing. Gregory Crouch’s Enduring Patagonia (New York: Random House, 2001) details one mountaineer’s experiences on Fitz Roy and Cerro Torre.
Backpackers should note that no campfires are permitted within the park—carrying a camp stove is obligatory for cooking. Wildlife includes the endangered, rarely seen Andean huemul.
As the Pleistocene ended and the Campo de Hielo Sur receded, it left behind the two huge glacial troughs that are now Lago Argentino and, to the north, the roughly parallel Lago Viedma. While these lakes lie only about 250 meters above sea level, the Andean summits along the border rise to 3,375 meters on Cerro Fitz Roy and nearly as high on pinnacles such as 3,102-meter Cerro Torre, which match Chile’s Torres del Paine  for sheer majesty.
Most of these bodies of water lie beyond park boundaries, but the eastern Andean slopes still contain their remnants, some of the world’s most impressive, and accessible, glaciers. Thirteen major glaciers flow toward the Argentine side, including the benchmark Moreno Glacier ; ice covers 30 percent of the park’s surface.
Despite its accumulated snow and ice, the Argentine side is drier than the Chilean, receiving only about 400 millimeters of precipitation on the eastern steppe, rising to about 900 millimeters at its forested western elevations. The warmest month is February, with an average maximum temperature of 22°C and a minimum of 9°C; the coolest is August, when the maximum averages only 5°C and the minimum is -1°C. As elsewhere in Patagonia, it gets ferocious winds, strongest in spring and summer.
Where rainfall is insufficient to support anything other than coirón bunch grasses and thorny shrubs such as the calafate (Berberis buxifolia) that gave the nearby town its name, the guanaco grazes the Patagonian steppe. Foxes and Patagonian skunks are also conspicuous, the flightless rhea or ñandú scampers across the open country, the bandurria (buff-necked ibis) stalks invertebrates, and flocks of upland geese browse the swampy lakeshores. The Andean condor soars above the plains and even the highest peaks, occasionally landing to feast on carrion.
In the forests, the predominant tree species are the southern beeches lenga and the coigüe, also known here as guindo. The puma still prowls the forest, while the huemul and perhaps the pudú survive near Lago Viedma. Squawking flocks of austral parakeets flit among the trees, while the Patagonian woodpecker pounds on their trunks. Perching calmly, awaiting nightfall, the austral pygmy owl is a common late-afternoon sight.
Along the lakeshores and riverbanks, aquatic birds such as coots and ducks are abundant. The most picturesque is the Patagonian torrent duck, which dives for prey in the rushing creeks.
At the Río Mitre entrance, the main Moreno Glacier approach, the Administración de Parques Nacionales (APN) collects a US$17 admission fee (payable in pesos only) for nonresidents of Argentina. At present, the Lago Roca  and El Chaltén  sectors continue to be fee-free.
At the southern approach to El Chaltén, the APN (tel. 02962/49-3004, 9 a.m.–8 p.m. daily) has turned a former hostería into a visitors center. In addition to natural history exhibits, it provides a decent trail map (scale 1:75,000) and also issues climbing permits (free).
The Moreno Glacier  is about 80 kilometers west of El Calafate  by RP 11, which is now completely paved; the trip takes slightly over an hour. Both Cal Tur (tel. 02902/49-1842) and Taqsa (tel. 02902/49-1843, www.taqsa.com.ar ) at El Calafate’s bus terminal, have scheduled services at 9 a.m. daily (US$23 round-trip), returning in the afternoon.
In addition to regularly scheduled services, guided bus tours are frequent, but both are less frequent in winter. Competent operators include Aventura Andina (Avenida del Libertador 761, Local 4, tel. 02902/49-1726, andina [at] cotecal [dot] com [dot] ar), Cal Tur (Avenida Libertador 1080, tel. 02902/49-2217, www.caltur.com.ar ), Cordillera del Sol (25 de Mayo 43, tel. 02902/49-2822, www.cordilleradelsol.com ), Eurotur (Avenida del Libertador 1025, tel. 02902/49-2190, www.eurotur.com.ar ), Mundo Austral (Avenida Libertador 1114, tel. 02902/49-2365, mundoaustral [at] cotecal [dot] com [dot] ar), and Rumbo Sur (9 de Julio 81, Local 2, tel. 02902/49-2155, www.rumbosur.com.ar ).
El Calafate’s Albergue del Glaciar runs its own guided minivan excursions (US$50 pp), leaving about 8:30 a.m. and returning about 5 p.m. These include more hiking and a navigation for a waterside view of the lake.