Aconcagua is the highest mountain in South America, in the western hemisphere, and in the southern hemisphere, too. No other peak on earth, except Mount Everest, is further away from a higher peak--you have to travel over 10,250 miles to the Hindu Kush Mountains of Pakistan to find higher ground when traveling from Aconcagua.
There have been occasional noises made by the Argentines and others that
Aconcagua might be over 7000m high, but it seems that the consensus is that it falls just short, leaving all the world's 7000m peaks in central Asia. An Italian expedition in 2001 with super-accurate GPS equipment has fixed the peak's elevation at 6961.83 meters.
The mountain is geologically complex, and while many of the rocks that form it are volcanic, the general feeling seems to be that Aconcagua is not an eroded, long-dormant volcano, as one might suppose. That leaves Ojos del Salado, in the Puna de Atacama well north of Aconcagua, as the world's highest volcano.
The peak is located 15 km east of the main crest of the Andes, entirely in Argentina. This is the dry side of the Andes, so, despite its height, Aconcagua is not particularly icy or snowy. The standard routes up the mountain involve no glacier travel. The area is not as arid as the bone-dry Puna de Atacama, but the glaciation is less than in the Andean peaks of Peru and Patagonia.
With a city of 4 million (Santiago, Chile) 100 kilometers away, and with the major trans-Andean highway from Santiago to Mendoza, Argentina passing just south of the peak, access is easy to Aconcagua. The standard route is just a long hike, and by far the greatest difficulty is the high elevation. Altitude sickness kills unacclimatized climbers on this mountain, so it is important to go up slowly. The other main danger is storms--Aconcagua is exceptionally windy, and one must be prepared to wait out bad weather.
Two weeks is the recommended minimum time it would take to fly there from the USA and do the hike, and three would be better. Aconcagua makes an attractive destination: there is no easier way to climb to 6900m in the world, nor is there an easier peak with more prominence or isolation.