A supplemental of sorts to The Operative Word (Sam/Dean, 33k, E, post-series fic for the prompt fuck or die).
Here is the Holy Grail quest of Galahad as adapted by John Cooney and drawn by Alex A. Blum for Classics Illustrated #108, Knights of the Round Table, June 1953-the comic Sam describes Dean reading to him in 08x21, "The Great Escapist":