The former blast furnaces at Hattingen are open to the public. Visitors can buy a ticket and are then free to roam where once large machinery moved cokes and metal. All the way down the concrete cokes pits, all the way up the steel blast furnace towers.

I like this photo because however small each of the doorways is you get the idea of the vastness of the facility.

From the Heinrichshütte 2013 series