Take nothing but photos, Leave nothing but footprints.
Urban Exploration is the exploration of manmade structures, usually abandoned ruins or hidden components of the manmade environment. Photography and historical interest/documentation are heavily featured in the hobby, sometimes involving trespassing onto private property.
Ventures into abandoned structures are perhaps the most common example of urban exploration. Many sites are entered first by locals and may have graffiti or other kinds of vandalism, while others are better preserved. Although targets of exploration vary from one country to another, high-profile abandonments include amusement parks, grain elevators, factories, power plants, missile silos, fallout shelters, hospitals, asylums, prisons, schools, outmoded and abandoned skyscrapers, poor houses, and sanatoriums.