Okay. Take a planet. Now make it entirely artificial. But not made out of metal beams and such, made entirely out of trillions of Sentinels linked together. Then, at the center of the planet you have a portal. Take a step through the portal. You are now in a slipspace bubble the size of a person. However, that's not what you see since you're inside of it. You look around. There's a star about the size of our star. Surrounding it is an inverted planet that you are standing on. Where you're standing is the same distance the Earth is from the sun. You are inside a Dyson sphere. You start to explore. You encounter more portals that lead to more realms held by slipspace and compressed to a very small size in real-space. Time passes slower in slipspace. The deeper you go onto these realms, the faster time goes by in realspace compared to what you're experiencing. And that is Onyx.

If the star is the size of our star, the inverted planet must be huge.... Like billions of square miles of landmass... [spoiler]I just did some rough (probably incorrect) math based of the distance to our sun and it puts the estimated surface area of onyx at over 85,000,000,000,000,000 square miles. Damn[/spoiler] Unless it is some weird slip space physics thing. In that case never mind.

It's absolutely massive.. It's got a diameter of 2AU.

So in theory, could the entire human race comfortably inhabit onyx?

Then what is treyvan

Trevelyan is the name of the ONI research facility stationed in Onyx. Of course, the section of Onyx in real space that was comprised of Sentinels has been destroyed. So the Dyson Sphere has been brought to real space for ease of access.