I thought they would be like the pitfall traps from animal crossing/SSBB, but your descriptions sound more like L-space.

Obviously, the inside of a plothole contains things that cannot be described with feeble human words.

Many of the plot holes I've heard talked about didn't have any volume to speak of--they simply led from one place to another, connecting those two places without actually creating any extra space for the plothole itself.

It could be that plot holes which "contain" things may simply be plot holes that link to a space that does contain those things (and which may or may not be created along with the plot hole). There's lots of precedent for various places and objects being created out of nothing; a plot hole leading to a space that's been created by a fic probably wouldn't be out of the realm of the possible.

So plot holes may not be "holes" like the kind you might dig in the ground at all; they may be more like portals.

Some of them are like conduits--they allow for characters to have things they shouldn't have, or get to places they shouldn't be. This is the type that HQ has adapted and stabilized to connect the various parts of itself and to make portals

Others, like the ones canon characters end up inside when they get replaced, are just random pockets of misplaced space-time. This type is occasionally harnessed, as in the case of hammer-space/mace-space, Bags of Holding, etc. Generally I would think there's nothing inside except what someone puts there. There might not even be breathable air unless there's an open way in--but then again, there might be.

That's my two cents.

~Neshomeh

Given that most badly-described or inconsistent things in badfic default to Generic whatever.

Plus HQ harnesses plotholes as part of its architecture, so perhaps the Generic Surface is the result of the plotholes?

That said, they're plotholes, and governed by the Laws of Comedy and so if you need a plothole to be something for the purposes of a joke, I think that would be fine.

From what I understand, plotholes are basically roughly torn holes in reality, so I guess that there could be just about anything in one....

Just my thoughts on the matter.