In Indiana Jones and the Last Crusade, when Indy is going through the cave to get to the grail, he goes through several different obstacles. Either my memory is wrong or he was muttering to himself about different "clues" on how to get through. What were these "clues" and where did they come from?
The three challenges were:
The Breath of God - "Only the penitent man will pass"
The Word of God - "Only in the footsteps of God will he proceed"
The Path of God - "Only in the leap from the lion's head will he prove his worth"
Indy used his father's Grail Diary to guide him through the traps:
The Grail Diary was a possession of Doctor Henry Jones, Sr. In it, he recorded all of his findings on the topic of the Holy Grail, the study of which he had made his life's work.
He did many travels between America and Europe, contacted many scholars and sought several historical documents during his studies, always carrying it with him.
Indy's knowledge of his father's research in the diary helped him slip past the traps in the Grail Temple and recover the Grail to save his wounded father.
(the above images are from this site, which contains an extensive amount of information about the diary)
The clues came from the the Chronicles of St. Anselm. Professor Jones found them there and wrote them into his Diary
Professor Henry Jones: Well, he who finds the Grail must face the final challenge.
Indiana Jones: What final challenge?
Professor Henry Jones: Three devices of such lethal cunning.
Indiana Jones: Booby traps?
Professor Henry Jones: Oh, yes. But I found the clues that will safely take us through them in the Chronicles of St. Anselm.
Indiana Jones: [pleased] Well, what are they? Can't you remember?
Professor Henry Jones: I wrote them down in my diary so that I wouldn't have to remember.