The act of exploring locations that are abandoned. An urban explorer will be one who goes to locations to take pictures, video or just to look.
Someone who goes to an abandoned location to commit vandalism or other kinds of illegal activity (besides trespassing) should not be confused with an urban explorer.
Urban exploring is not just limited to "urban" areas.
Urban explorers usually follow the rule of:
Take nothing but pictures...
Leave nothing but footprints...
Break nothing but silence...
Although this rule is commonly broken in a way that people will sometimes take items for a personal souvenier. This is something that does not bother most unless things are taken in mass quantities for a profit.
Hey, what do you want to do today?
-How about we go to that abandoned hospital to take some cool pictures!
Okay, sounds cool... I love urban exploring!