Hiking generally refers to walking on different terrains, typically in natural environments, which can include trails, mountains, forests, and other outdoor areas. While having a designated hiking route and going with a group can enhance the experience, they are not strictly necessary to define an activity as hiking. Spending the night in a sleeping bag is related to backpacking or camping, which can be part of hiking but is not a requirement of the activity itself. Thus, the best answer in this context would be:
Walking on different terrains.