Urban exploration (often shortened as urbex or UE) is the examination of the normally unseen or off-limits parts of urban areas or industrial facilities. Urban exploration is also commonly referred to as infiltration, although some people consider infiltration to be more closely associated with the exploration of active or inhabited sites. It may also be referred to as "draining" (when exploring drains) "urban spelunking", "urban caving", or "building hacking".

Many explorers find decay of uninhabited space to be profoundly beautiful and some are also proficient freelance photographers. Abandoned locations can be, at times, heavily guarded with motion sensors and active security. Others are more easily accessible and carry less risk of discovery. An important goal, overall, of exploring a location is to gain access, perform your task, and remove yourself undetected, unscathed, causing no harm to others or that which surrounds you. Abandoned sites are also popular among historians, preservationists, architects, archaeologists, industrial archaeologists, and ghost hunters.

(wikipedia - "Urban Exploration")