Pittsburgh Ruins

I was walking along a street in Pittsburgh - a little out of the way, but with bus stops & highway overpasses & an electric company employee snoozing in his truck - when I came upon a whole row of ruins. Houses torn down when the highway went in? Or just a remnant of Pittsburgh's declining population? They are beautiful and mysterious, and quite unlike the glossiness of the cultural district or the funky working neighborhoods in other parts of the city. It feels a little like a place where people shouldn't be, just let the ruins slump back into the earth.