I found this plugin they used on another server, Multiverse, which lets you have more worlds like the overworld/nether/end, so we could have e.g. a creative world and an amplified world and so on.
Multiverse, the best world management plugin for your server!
The Bukkit World Management Plugin.
I was going to test install it to see how it works. Any opinions on whether we should use it and how the extra worlds should be?
If installed, it was my idea to have portals to the extra worlds be in special locations like Desertopia, Aahrus etc. to put some special features and incentives to go around the world.
It won't be installed if it appears to cause problems with how worlds are saved (in a way that could ruin them if the plugin becomes outdated or is removed again).