Apartment 3B was located on 1121 South Kelsey Street, in Hill Valley, California. Doctor Emmett Brown lived here in the 1940s.
In 1945, the building burned down, and the blueprints for Doc Brown's inventions were destroyed in the fire. When Doc Brown demonstrated his Fance-O-Dance mechanical automatic dancing shoes for his son, Verne, in 1992, they burned out, and Doc couldn't fix them without the blueprints. Marty McFly and Verne traveled back to September 27, 1944 to retrieve the blueprints from Doc's apartment.