Captain Antilles said:

You acknowledge that Vader is merely a manifestation of Luke's mind, so why can't the "structure" around him be a part of this manifestation, as well? I mean, that's how I've always thought of it. You say that it should be just a cave, nothing more, and I agree completely! The difference, though, is that I think it IS just a cave--a cave that's strong with the dark side of the Force. Given the negative energy swirling within it, maybe its appearance changes depending on who enters it. Think of boggarts from Harry Potter--it's the same general concept.

I hear ya, CA. It could be a part of that. But if I were to do that, I'd show it to the audience. I'd show the cave transform. Have it change right around Luke. After that, I'd show the fog start to appear and... well, you know the rest.

But I can understand the other points of view. Seeing some sort of structure there without an explanation appeals to the imagination of what it might have been.

Bingowings said:

He takes fear and doubt into the cave and it shows him the object and the consequences of his fear.

Excellent.

timdiggerm said:

Lemonstein said:

That's totally wrong. At no point is it said that Luke is in control of what he "takes with him" into the cave.

You mean other than the very symbolic part where Yoda tells him he won't need his weapons and he chooses to take them in, right? Yeah, you can say that Luke's choosing the weapons betrays the unconscious, the desires and emotions he can't control, but I think the more valid (within the philosophy of Star Wars, of course) view is that by choosing the weapons he also chooses the attitudes revealed by content of the vision.

Exactly.