The Los Glaciares National Park covers 600,000 hectares (1.5 million acres) of rugged land that stretches vertically along the crest of the Andes and spills east into rolling steppe. Most of Los Glaciares is inaccessible to visitors except for the park's two dramatic highlights: the granite needles, such as FitzRoy near El Chaltén (covered in "El Chaltén & the FitzRoy Area"), and this region's magnificent Perito Moreno Glacier. The park is also home to thundering rivers, blue lakes, and thick beech forest. Los Glaciares National Park was formed in 1937 and declared a World Heritage region by UNESCO in 1981. It is a wild, rugged, and yet sublimely beautiful landscape -- one that offers up surprise, wonder, adventure, and serenity all at once.

Named after famed Argentine scientist Francisco "Perito" Moreno ("perito" is the title given to someone considered an expert in their field), the famous glacier Perito Moreno is a must-see, as important to Argentine culture and tourism as Iguazú Falls or the Casa Rosada. Few natural wonders in South America are as spectacular or as easily accessed as this glacier. It's just one fingertip in the imposing Patagonian Ice Cap, the fourth-largest frozen mass in the world after the two poles and Greenland. Perito Moreno is one of the few glaciers in the world that is not receding. Scientists like to say that it is "stable," or constantly growing and receding. Around 1900, Perito Moreno was measured at 750m (2,460 ft.) from the Península Magallanes; by 1920, it had advanced so far that it finally made contact with the peninsula where tourists now walk the lovely and newly refurbished boardwalk and take in views. Each time the glacier reached the peninsula, which would occur every 3 to 4 years, it created a dam in the channel that drastically altered water levels on either side. Over the period of a few years, the built-up pressure would set off a calving explosion for 48 to 72 hours, breaking the face of the glacier in a crashing fury. The last time this happened was in July 2008, making news across the country. Perito Moreno is usually reliable for sending a few huge chunks the size of buses hurling into the channel throughout the day. Sit in silence with your camera ready and you're almost certain to get a fabulous photo opportunity of a calving glacier.

What impresses visitors most is the sheer size of Perito Moreno Glacier -- a wall of jagged blue ice measuring 4,500m (14,760 ft.) across and soaring 60m (197 ft.) above the channel. You literally could fit the entire city of Buenos Aires on it. From the parking lot on the Península Magallanes, a series of vista-point walkways descend, which take visitors directly to the glacier's face. It's an unforgettable, spellbinding experience, worth taking in slowly so you can savor the view and capture the ice cracking off in photos or videos. You can join an organized group for a walk on the glacier, and there are boat journeys leaving from Puerto Banderas for visits to the neighboring glaciers. In 2008, a major infrastructure expansion project began at the Península Magallanes, and already includes refurbished boardwalk paths and a new cafeteria. Down the hill, at the dock, there's another large restaurant and a giant visitor center in the works.

There are other magnificent glaciers in the national park, all much harder to access than Perito Moreno but equally stunning. The Upsala Glacier is the largest in South America, and the Spegazzini Glacier has the largest snout of all the glaciers in the park. Onelli, Seco, and Agassiz are also gorgeous. All can be seen as part of the All Glaciers Tour, organized by René Fernández Campbell, whose main office is at Av. del Libertador 867 (tel. 02902/492340).

Glaciology 101 -- A glacier is a large body of snow and ice that slowly moves down a valley or spreads across a surface due to accumulation and gravity. Glacial ice forms when heavy snowfall crushes first into snow crystals and then into pellets, finally becoming a dense mass that takes on transparency and hardness over time. Heavy precipitation and low temperatures are the most significant factors in glacial growth. Dark lines in the glaciers, called moraines, are produced by rock debris, sand, and clay that accumulate on the ice. They are useful for indicating past positions of the glacier.

Note: This information was accurate when it was published, but can change without notice. Please be sure to confirm all rates and details directly with the companies in question before planning your trip.