Space
Danny had always dreamed of space.
He had dreamed of flying to Mars on a rocket ship, of visiting Alpha Centauri and exploring what worlds the binary star system has to offer, of seeing the Pillars of Creation with his own two eyes, of traversing the depths of a black hole to find just what lay on the other side of its event horizon.
Of course, most of these dreams were pipe dreams. The Pillars of Creation were 7000 lightyears away; the nearest black hole, 3300 lightyears away in the Monoceros constellation. Even Alpha Centauri, the nearest star system to the Solar system, took 4.3 years to reach traveling at the speed of light. There was no way humanity would invent faster than light travel before Danny was old and gray. So he had set his sights on Mars, on joining NASA's ranks and setting himself up for a trip that could only be made every 26 months, a trip that would take 234 days using Hohmann transfer, a trip that would place him among the first to set foot on another planet.
Now, of course, even that was a pipe dream.
With his grades— hell, with his biology, if you could call it that— how could he hope to join the ranks of NASA? Even if he somehow pulled his grades up enough for them to consider him, he'd never make it past the initial health screening. Even if they didn't send him to the nearest lab for "lots and lots of painful experiments", who would trust a freak of nature like him to join a team of NASA's elite? Except for experimentation, why would anyone send a ghost to space?
But the more time he spent in the Ghost Zone, the more he realized he didn't need NASA to go to space. Space was right here.
In space, stars were born, and lived, and died. And as their lives left an imprint on the universe, so too did their deaths leave a mark upon the Ghost Zone— the remnants of white dwarves peppering the infinite realms, outshone by supernovae forever exploding bright green, spilling ectoplasm into the Ghost Zone. Portals shown like stars, twinkling in and out of existence, forming ever changing constellations against the endless swirling green. When they collided, ectoplasmic dust flew from them, swirling and spiraling and adding to the flow of the Ghost Zone, forming nebulae in which ghosts and lairs and islands were born.
And all of it sang. The supernovae gushing, the portals spinning and colliding, the nebulae drifting, the Ghost Zone itself flowing and swirling in a dance only ghosts seemed to understand— a dance they were a part of, dancing to the musica universalis, the dynamic equilibrium set in the give and take of the infinite realms. It was a dance Danny could feel inside himself, flowing through his veins and thrumming in his core. He couldn't explain it— didn't know how to tell Sam that the howling and static she heard was music to his very being, couldn't explain to Tucker how the meandering route he took from the Fenton Portal to the Far Frozen simply felt right in a way that cutting through the flow in a straight line didn't. They were human— they couldn't feel the music of the spheres in their own universe, let alone in a dimension of which they ultimately were not a part. Danny couldn't explain it, but he could feel it with every last molecule of his self. And most days, that was enough.
He sat atop the highest peak of an unclaimed island, feeling his molecules dance with the universe, gazing at the whirling, crashing, magnificent galaxies spinning above him. He thought about a book from Clockwork's tower that had caught his eye— the cover was black, but glinted with a hint of stars, of constellations he had never seen before. It claimed that at the center of every black hole lay a portal to the Ghost Zone.
As he stared, a portal formed, and then another. They crashed into each other, and the splash of ectoplasmic dust from their collision looked almost like the Pillars of Creation. The sound was music to his ears.
He had always dreamed of space.
Now he didn't have to.