Urban exploring is an art form. It's where you sneak into abandoned buildings like old hospitals or museums and examine what people left behind. True urban explorers are like archaeologists, and have this desire to preserve the past.
There's this whole underground community in cities all over the world, a lot of them belong to a kinda "clan" where they have fake names they call themselves and their own inside lingo.
No offense to Seabastion, but he seems a bit like an amateur, more like a creeper than anything.
Interesting fact: Walt Whitman was one of the first serious urban explorers, (I always thought this was kinda funny.)