An adventure is an exciting experience or undertaking that is typically bold, sometimes risky.[1] Adventures may be activities with some potential for physical danger such as traveling, exploring, skydiving, mountain climbing, scuba diving, river rafting or participating in extreme sports. Adventures are often undertaken to create psychological arousal or in order to achieve a greater goal such as the pursuit of knowledge that can only be obtained in a risky manner. Camping is an outdoor activity involving overnight stays away from home, either without shelter or using basic shelter such as a tent or a recreational vehicle. Typically participants leave developed areas to spend time outdoors in more natural ones in pursuit of activities providing them enjoyment or an educational experience. The night (or more) spent outdoors distinguishes camping from day-tripping, picnicking, and other similarly short-term recreational activities.[citation needed] Camping as a recreational activity became popular among elites in the early 20th century. With time, it grew in popularity among other socioeconomic classes. Modern campers frequent publicly owned natural resources such as national and state parks, wilderness areas, and commercial campgrounds. In a few countries, such as Sweden and Scotland, public camping is legal on privately-held land as well. Camping is a key part of many youth organizations around the world, such as Scouting, which use it to teach both self-reliance and teamwork.