I think he started traveling around Europe meeting people n the urban exploration community a year or two ago. There was always an element of this in his videos, though - the first one I remember seeing was him sneaking into closed off floors of a semi-abandoned mall, finding what appeared to be a murder-size pool of blood (but was hopefully just really stagnant water or something) on an upper floor, and then hurrying out without saying anything.
Wow, his channel has some pretty extreme stuff now. Back when I used to submit his videos, he seemed like the kind of guy who almost never leaves the house.
I once typed my work address into YouTube and the first result was one of these elevator people just riding up and down. Everyone at work thought it was creepy as hell.