Oh COME ON! I thought **EVERYBODY **knew the truth of the Holy Grail!!!
The truth lies in the cave of Caerbannog, wherein, carved in mystic runes upon the very living rock, the last words of Olfin Bedwere of Rheged make plain the last resting place of the most Holy Grail.
Those who venture within (braving the rabbit and the beast) will discover that Joseph of Arimathea testified that the Grail may be found in the Castle Aaagh. Of course, you must cross the Bridge of Death to get there. It helps to know about swallows (especially African and European varieties), but, of course, only kings are expected to know these things.