Adventure travel is a type of niche tourism, involving exploration or travel with a certain degree of risk (real or perceived), and which may require special skills and physical exertion. In the United States, adventure tourism has grown in recent decades as tourists seek out-of-the-ordinary or "roads less traveled" vacations, but lack of a clear operational definition has hampered measurement of market size and growth. According to the U.S.-based Adventure Travel Trade Association, adventure travel may be any tourist activity that includes physical activity, a cultural exchange, and connection with nature. Adventure tourists may have the motivation to achieve mental states characterized as rush or flow, resulting from stepping outside their comfort zone. This may be from experiencing culture shock or by performing acts requiring significant effort and involve some degree of risk, real or perceived, or physical danger. This may include activities such as mountaineering, trekking, bungee jumping, mountain biking, cycling, canoeing, scuba diving, rafting, kayaking, zip-lining, paragliding, hiking, exploring, canyoneering, sandboarding, caving and rock climbing. Some obscure forms of adventure travel include disaster and ghetto tourism. Other rising forms of adventure travel include social and jungle tourism. Access to inexpensive consumer technology, with respect to Global Positioning Systems, flashpacking, social networking and photography, have increased the worldwide interest in adventure travel. The interest in independent adventure travel has also increased as more specialist travel websites emerge offering previously niche locations and sports. History Since ancient times, humans have traveled in search for food and skills of survival, but have also engaged in adventurous travel, in explorations of sea lanes, a destination, or even a new country. Adventurer travelers began to push to the limits, with the mountaineering of Matterhorn in 1865 and the river rafting on the Colorado River in 1869. Shortly after, two key institutions were formed, including the National Geographic Society and the Explorers Club, which continue to support adventure travel. At the end of World War II, modern adventure began to take off, with 1950 French Annapurna expedition and the 1953 British Mount Everest expedition. Today, it remains a niche of travel and a fast-changing sector with new variants of activities for a travel experience. Types Accessible tourism There is a trend for developing tourism specifically for the disabled. Adventure travel for the disabled has become a US$13 billion a year industry in North America. Some adventure travel destinations offer diverse programs and job opportunities