Hidden unknowns

Doors in the outer yard at Eastern State Penitentiary in Philadelphia, Pennsylvania.  The prison was built in 1829 and closed in 1971 remaining abandoned for several decades before being re-opened to the public as a tourable historical attraction. 

Technical Details:
Nikon F4S 35mm film camera.  Nikon 18-35mm F3.5-4.5 AIS lens.
Ilford Delta 100 film shot at ISO 100. 
Developed in Diafine for 4 minutes (part A) and 4 minutes (part B) @ 20 degrees Celsius in Paterson 3 reel tank.  5 seconds initial agitation with swizzle stick followed by 5 seconds of additional agitation every minute thereafter. 
Negative scanned with Epson 4990 on holders with ANR glass.