Concept:
The actual realm of imagination is involved, and is central to all knowledge while at it.
Description:
An intra-/exo-reality (kinda both simultaneously, really. With our reality between them.) nexus that is a reality unto itself (like another dimension of anything and everything, no limits; also kinda works like The End of Time in Chrono Trigger for intersecting realities). Kinda like if reality was made up of bubbles, this is the center of the 3D/4D-Venn Diagram of those bubbles (Star Trek meets Star Wars, Lexx, and the like; with Tolkien and such also tossed in to spice it up a tad. So what if my dragon breathes lasers that can home in on it's targets (Panzer Dragoon)?). Our imagination when utilized for invention and telling stories and such only merely taps into this reality. Someone finds a way into this reality, which is anything but real. Just as well; for anyone that wants a "political aesop" for this; The "Copyright Police"/Fun Police have captured this realm, and is monopolizing it by restricting imagination within reality, preventing anyone from thinking again; or some BS like that. Just as well, unimaginative trolls or die-hard uber-realists also bash any new concept brought upon by said realms due to how unrealistic they are (albeit, they would have a point, but where said things come from, I don't think the beings/devices from said realm care about the concept of realism), or just because they're total douchebags that can't come up with anything new, and rattle off memes nonstop. Plus, I doubt science can explain even an iota of these things, and how they're waltzing about our reality without being crushed under their own weight and such. Or how a lightning gun isn't frying it's operator when fired; or how fire is freezing things... The list goes on.
Source:
South Park and Rick & Morty had similar concepts, more or less. Oddly enough, Muppet Babies is a core reference (say what you will, it was an awesome show back then). I don't remember if they dove into an imagination world/nexus before, but they were practically reality-warpers with all the crazy stuff they did with their imagination; for example, I remember Scooter's computer was practically able to hack reality itself. He was as good a programmer with his computer as Schroeder (Peanuts) was with his piano. Hell, they were able to share thoughts/imagination clearly with minimal explanation, as if they were psychic, yet unaware of it. They could see each others' thoughts without aid.
Alt-Source:
My mind works like this at times. Not as much as it used to; but I'm working on reviving that (actually, I'm trying to make it happen again during Lent; see if I can replicate what started it in the first place). It was equally awesome and terrifying; in a good way. I called that realm the "Second Nature" as a means of expressing how naturally it occurred, and it also being an ever-present and constantly evolving realm, much like ours. Much of my art rendered what I saw within there. Funny enough, I think a marking I made apparently followed sacred geometry, before I was aware of such, that also felt like a map to the place. 3 points, 3 lines, 3 circles. The circle containing the triangle and inner circle also has the 3 points that anchor the triangle to the mid-circle, while it contains the inner circle. An outer-circle contains all of that, like a container. Thus, the intra-reality (inner circle, bound by the triangle), reality (mid-circle, containing the triangle anchored by the points), and exo-reality (outer circle, containing everything else within). I'll post it if I can find it. Basically, it was my own take on the triquetra.
EDIT:
Just remembered, plenty of my dreams are basically involving this concept more directly. Kinda why I'm such a screwball once I go lucid. It's like finding out the God Mode in games is actually more like unlocking Garry's Mod instead of gaining invulnerability. Full-integration of GMod-level imagination application upon our own reality (summon/modify/involve other games and such; lethal vuvezelas), is basically what my concept is. Not to mention, the very realm of imagined thoughts and such is it's own melting pot reality.