On a previous trip to Pueblo Colorado, I had tried photographing these doors with my pre-1940's camera. It wasn't very successful. On a return trip I tried again. I used my Mamiya 7 and Ilford SFX 200 film with a 695 filter. I am considerably happier with these results.
These doors were the entrance to the Pueblo Steel Mill. They connected to a tunnel that went under a busy rail line servicing the Mill. Today the rail line has been replaced by the busy interstate 25. I was told at the museum that the tunnel is still connects to the other side, but was unable to confirm it.