Trekking is an activity in which people take multi-day hiking trips through rural, often rugged territory. Many people who are trekkers engage in longer trips through entire regions of the world, using trekking as a way of getting from place to place. It also can be incorporated with other outdoor sports, such as rock climbing or backpacking. Trekking can be done anywhere in the world. Certain areas are particularly popular with trekkers, including mountainous regions such as the Himalayas in Asia and the Andes in South America. Treks also have been organized in other less-visited areas on almost every continent. This activity is different from other types of travel for several reasons. It tends to be less structured than other sorts of travel, because weather conditions and topography can influence trekkers’ travel plans more than plane flights or hotel availability.