In my town was an abandoned and decaying industrial estate, completely accessible with no attempt to fence it off. It had been used as a canvas by graffiti 'artists', and some of it was pretty good. there was an old railway line too.
Last year, i heard it was scheduled for re-development for houses, so i grabbed my camera and tripod and walked down there. It was still intact, and i returned a week later for some more images. I thought of producing a series of the area through the seasons, and it would have been fab in infra-red.
A fortnight after that first visit, i returned to find the place fenced off with eight-foot high fencing, thus totally inaccessible, and the week after, it had been demolished. So i was glad I visited it when i did, but wish to heck i'd taken the opportunity to visit earlier.