Urban exploration (often shortened as UE, urbex and sometimes known as roof-and-tunnel hacking) 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 and it sometimes involves trespassing onto private property. Urban exploration is also called draining (a specific form of urban exploration where storm drains or sewers are explored), urban spelunking, urban rock climbing, urban caving, building hacking, or mousing.