Ok, I noticed some very intelligent answers on this platform and I would love your input on the planet for my book trilogy. I have been working on the blueprint, story structure, and characters for years and I am ready to start writing the book format soon. The last thing I want to cover is to make the planet more 'believable'. Let's agree that it doesn't have to be correct. I just need it to be believable. Like we believe the Death Star in Star Wars or the Halo in Elysium or... Halo.
For my peace of mind I will try to explain without giving away to many details.
The planet would exist in a piece of dead space. It has to be unreachable and inescapable with no stars or planets anywhere nearby. (Because a large part of the galaxy around it has been destroyed a long time ago in order to create the base of this planet that should never be found).
Life on the planet should be possible. But like I said. There are no stars. Instead, I envision a big artificial moon with a big light source that would look like a prison searchlight directed at the planet. This light source should be designed to emit just the right amount of energy to enable life on the planet.
The planet should be inescapable. Even for lifeforms that can teleport or fly or build a space ship. I'm open to suggestions. Maybe by some kind of electromagnetic atmosphere or gravity that increases as you move further from the surface. (I know it works the other way around but like I said... I need to make it believable and I need al of the above to be possible for the sake of my story).
Finally, the core of the planet is used to imprison a huge entity. Between the surface and the core I would need another barrier that prevents something very powerful from breaking out of use its powers to influence the surface. The core should be reachable by human-sized tunnel systems though.
I left out a lot of context to guard my concepts, but I'm very exited to learn more about how this kind of artificial planet would be 'possible'.
Kind regards and thanks for your time and interest, Luke