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.

The nature of this activity presents various risks, including both physical danger and the possibility of arrest and punishment. Many, but not all, of the activities associated with urban exploration could be considered trespassing or other violations of local or regional laws, including—but not limited to—invasion of privacy and certain broadly-interpreted anti-terrorism laws.