Travelers will encounter just about every climatic zone in Bolivia, from stifling humidity and heat to arctic cold. Summer (November to April) is the rainy season, when overland transportation becomes difficult if not impossible in some areas. In the lowlands it can be utterly miserable, with mud, high humidity, biting insects and relentless tropical downpours. The most popular, and arguably most comfortable, time for exploring the whole country is during winter (May to October) with its dry, clear days. This is also the best season for climbing. 

The high tourist season falls between late June and early September, due not only to climatic factors, but the timing of European and North American summer vacations and the fact that it's also Bolivia's major fiesta season. Both international visitors and lots of South Americans are traveling during this period, so prices are generally higher than during the rest of the year.