What will truly happen when Jon goes down into Winterfell's crypts?!

[TheUnknownTargaryen]

Whether it's in a dream, in Ghost, or awake Jon, what do you think he will see or happen?

It's by far, one of the moments I can't wait to read. I'm excited to see if he talks with Ned or Lyanna. If that's where he learns of his parentage. Maybe there is Torrhen's crown or Rhaegar's harp. Will Lyanna convey to him that he is TPTWP? Whatever it is, I can't wait!!~!

[King Jaime Lannister]

I agree with the harp theory. Could see the crown as well.

I wonder if it will be Jon himself or another character?

[Arthur Dayne's Honor Alt]

The physical proof of his heritage is probably in Lyanna's coffin. I also think he will wander through a dream world, maybe the spirit world of the Old Gods, and will talk with Ned, an maybe Lyanna and Rhaegar. Similar to how King Arthur spoke to his mother(or father) and find out he was the rightful king.

[assjfjgjsgjljljglgjfjsduar]

I think the crypts will be the symbolic location of Jon's catabasis, which he's right on schedule to undertake after being stabbed. Whatever "boon" he finds there (and if it's symbolic and appears to him in a dream/coma, then the boon would be intangible, probably information) will help him as he enters the endgame of his journey.

I do think that something concrete exists in the crypts that will have implications for Jon; too much has been teased about it and the crypts keep coming up again and again. But I think that might be separate from the catabasis, or perhaps he'll discover something during the catabasis that will come up in person later.

An aside ... but for all the talk of GRRM subverting tropes and bucking fantasy conventions, Jon at least is following a pretty standard Campbellian hero's journey.