See also
Tarot symbolism
Mystical Places
The Holy Grail
Source mythology
The Green Knight Sequence

The boys face four Grail challenges, each related to the suits of the minor arcana and their symbolism.

Coins or Pentacles/Earth/diamonds. The physical world, wealth, health.
* The first item they recover is the dish (big enough to use as a shield?), at America’s Stonehenge in NH.
*They have to descend underground, and what holds Dean back is the pain from his stab wound (this doesn’t hold him back, of course).
*They hear the minotaur there but don’t confront him.
*Maybe Lorcan’s thugs meet them, and offer to buy the cup? Or afterwards they meet Lorcan himself, who offers them riches in exchange for the cup. (Maybe he comes in their dreams?)
**And Dean tells Maya (or Lily?) and she gives them malachite to protect them.

Swords/Air/spades. Intellect, the head.
*The second item is the sword, possibly Excalibur/Caliburn.
*They go to Chicago, where they are taken up into the second city and meet the Green Knight, who threatens to cut off their heads if they don’t answer his riddles correctly.
**because if any city deserves a second version, it’s Chicago.
*They may also be distracted by visions of lost loved ones or other illusions: it’s a dream-city, with many temptations.
*I’m seeing this happen in a club (called the Hanging Man? or the Green Man?) where the Green Knight holds court, as it were. There are a lot of hints that this isn’t ”quite” normal Chicago, but they never come out and say so.
**or it’s an inn between worlds kind of place, but reached through Chicago.
***they notice the pub is filled with otherworldly creatures (including those they usually hunt) and Sam remarks they’re not in Kansas anymore. “Not exactly the Emerald city, either,” says Dean.
**call it the Green Man and have a sign of either a headless man holding his head, or a man hanging from a tree by the foot
**How is he safe from Lilith? Is he? Should there be an interlude where she kills the Green Knight?
***or she could even be there, watching…

Wands/Fire/clubs. Will, passion, power.
*The second confrontation with Lorcan, possibly at Medicine Wheel in Wyoming.
*The item they’re recovering is the Spear of Destiny.
*Lorcan tempts Sam with power–perhaps realizing by this time that Lilith is not going to keep her promise, or attempting to deceive Sam, who sees through it but decides to claim his power on his own.
*They leave Dean in a fire to die, hanging, to be rescued by Castiel (and Bobby? Needs more Bobby.).
**Or, they just leave Dean in the fire, and the hanging bit comes later.
*If I’m using the Medicine Wheel, and I think I am, the fire should take place at the visitor’s center rather than at the wheel itself–I don’t even want to ”hint” at desecrating the place.

Cups/Water/hearts. Emotion, the heart.
*The final confrontation at Grace Cathedral in San Francisco, where Dean has to reclaim the cup, heal himself, and save Sam.
*It’s probably raining, this being SF–also it’s by the ocean, so there’s plenty of water. Raining everywhere but over the outdoor labyrinth at the cathedral, in fact? where Sam and Lilith are duking it out.
*And love, of course, is what powers the Grail.
*It’s also at this point that Dean asks and answers the Grail question: ”Whom does the Grail serve?”

The minotaur is present at all four locations, heard and smelled but unseen until Grace Cathedral. He can only be slain by the weapons they recovered along the way, either the sword or the spear.
*Or maybe he doesn’t need to be slain, but set free? Lilith has been using him to hunt the boys, and what needs to be done is sever her control over him.

Lilith can’t go to Medicine Wheel or inside Grace Cathedral, as they’re sacred places, so she sends the minotaur instead, who is bound by different rules, being an elemental (and non-Christian) creature.