This complexity of iron I-beams and other metalwork is from an early 20th century German steel mill, long since de-commissioned and designated a "historic site." The iron framework supported a monorail train which brought raw materials to the blast furnaces. I would have loved to see this whole complex in action, especially by night when the furnaces would glow from within like volcanic craters.
Brown technical pen ink on sketchbook page, 8" x 3", May 13, 2015. Darker areas added in Photoshop.