Data sharing
Yeah, I've had a look at the documentation. I also saw blessed hashes may be blessed in one thread but not in another. So I have to have a closer look at that.

Main threat that communicates with the objects
Your idea of the main threat maintaining the objects might be a good idea and I will consider it the most likely to use possibility for the moment.

One thread per NPC?
No, I was not intending to give every NPC its own thread. Actually, I only need two threads: one to take care of all NPC's (all NPC's are allowed to do their things one by one, maybe in a random order, maybe in order-of-appearance in the "realm"), one to take care of the human (well... let's hope so :D ) player.

thinking aloud mode
While philosophing a little about that, it might be a good idea to create a new thread whenever a new NPC has to be spawned. Then, within that thread, the first thing to do is to create a new instance of the appropriate class. But philosophing a little more, I come to the conclusion this will give problems when different objects need to get each other's data. This maybe might be solved by having subroutines in the main module that can access objects data. Although I do not quite see how to do this, it is worth to keep in mind, somewhere.

For now... thank you!
Good, it's late over here already and I am getting too tired to think straight, so I'll continue tomorrow. I've been playing around a little with programming different threads and I master the basics of it, so that part will not be too difficult.

So far, thank you all for all the hints, help and links to documentation you gave me!