If you are interested in urban decay, abandoned places or just in a plain sadistic mood, I’d recommend these two sites:
Övergivna platser by Jan Jörmark who teaches economic history in Gothenburg. Demographic and industrial changes have meant that Sweden has an abundance of abandoned plants, housing estates, highway motels and the like. I think that the series from the abandoned metro in Charleroi, Belgium, must be a personal favorite, though.
Some of the galleries need registration but Jörmark is not spamming, so it’s a safe option. And as Jörmark is a historian, the comments to the galleries are also quite enlightning.
The Dutch site Urban Exploration takes on the same topic but deals with urban decay in the Benelux.
Edit: More on the Charleroi metro here: In Search of King Louie – The Lost Rail Vehicles of Charleroi. The Dutch (!) wikipedia has a good section on the Charleroi adventure, including map.
Also: The Urban Exploration Ring.