The best time of the year to see South America really depends on where you plan on going. Typically, the very south of the continent - the countries of Chile and Argentina - experience four distinct seasons, with Patagonia in the very south of both best visited between December and February for the best weather.  The rest of South America typically experiences humid and hot weather conditions year-round, with countries close to the Equator and the tropics, such as Ecuador, Colombia, northern Brazil, Venezuela, and the Guianas maintaining consistently hot temperatures.  However, these countries have two distinct seasons: the rainy season and the dry season, with the latter far better for hiking in places like Huaraz, Machu Picchu, and national parks in Colombia and Ecuador. In most of South America, altitude also has a huge influence on temperatures, and you can expect a real drop in temperature when moving from lowland areas, such as Lima or Cartagena, up to areas with higher elevation, such as Cusco or Bogotá.