MLA

Steinberg, Saul, 1914-1999. Untitled [Castle]. Box 435, folder 5970. undated. https://collections.library.yale.edu/catalog/16849901.

APA, 6th edition

Steinberg, Saul, 1914-1999. (["Box 435, folder 5970"])(undated)[Untitled [Castle]]. https://collections.library.yale.edu/catalog/16849901.