NOTE: The Killion server is playable again on version 1.8.9
server address: killion.evolutiongaming.org

I used a mod to add "players" (NPCs) to the Prison, if you don't have the mod it still works, you just won't see the players I added. I encourage you to pick up where I left off. Let me know in the comments if you are going to work on this, I'd be interested to here it.

If you want to see what I did check here:
https://www.youtube.com/playlist?list=PL4pcAY7X0OxMbxA0j_J8629rDrvn8ZIl7

The server has a page on Planet Minecraft here:
https://www.planetminecraft.com/server/killion-detention-center---updated-100-prison-server/

What I downloaded to start can be found here:
https://www.planetminecraft.com/project/killion-multiplayer-server-map/

The mod can be found here:
the Link was removed: http://www.files.(Link removed) The website is called "NPCs - Mods - Minecraft - CurseForge"

The base for that mod can be found here:
https://files.minecraftforge.net/maven/net/minecraftforge/forge/index_1.12.html

I don't know how to upload it any better, just download everything (except Custom NPCs if you don't have that mod) and then put it in a folder called "Killion" and then put that in .minecraft/saves/ that should do it.