So as most of you know there’s a lot of unexplained stuff in Bionicle. At least there’s stuff I’ve never seen the answer to.
So I decided to post my theories for why those things happened.
First off: Why is there water around Metru nui?:
What if the island\city was actually floating? So when/if the robot flew too close to a gravitational pull the matoran wouldn’t fall the island/city would slowly position with the water.
Second:
Why does the inside of the Mata nui robot look like lush islands and citys?:
I believe this is so the matoran don’t realize that their doing work and think their just living. so they never question their work and have no reason to get bored.
Third:
Why are there rahi?:
So the simple answer is: The Makuta made them (I think) But you may remember Mata nui’s purpose. To research the universe and explore. What if the Rahi are mechanical versions of the aliens Mata nui encountered which the Makuta made so they could be put in the archives A.K.A. Mata nui’s living memory’s!
Are there any other unanswered questions in Bionicle? If so tell me.
No. The “water” around Metru Nui is actually called Protodermis, and it is inside the robot’s head.
Also, the island of Mata Nui was made by the great spirit robot as a cover-up that it landed there. The Toa Metru migrated the Matoran there to be safe from Makuta.
Also, the Rahi just happened to migrate to Mata Nui, and Makuta used infected masks on them in order to make them come under his control.
By water I meant protodermis:stuck_out_tongue 
And when I was talking about lush islands I was referring to Kara nui (I believe that’s the name)
And I was talking about why there was Rahi in the first place.
Mata Nui wanted Rahi there to just to populate the Matoran universe, that is all.
Karda Nui? That is inside the Great Spirit Robot, and is the heart of it. They sent the Mask of Life here to revive Mata Nui.
Yes and it had plants.
I believe the plants where there because Mata Nui wanted the islands to feel habitable. Although, a lot of the “islands” where actually cities with hardly any plant life.
Yeah the more inhabitable it seems the less riled up they’ll get for working.
The plant life grew in Karda Nui after the Great Cataclysm, didn’t it? I mean, there’s no way stuff could grow in there while it was a pulsing powerhouse of godly energy, so I’m pretty sure that was unintentional.
There are two technical “Karda Nui’s” one of them is the pre-cataclysm version, where the matoran were in their nice above ground villages and there was no swamp in the cavern below them. The. There’s post-cataclysm Karda Nui, in which the villages collapsed into the cavern, which also flooded with water from Aqua Magna.
Which one are we talking about here?
All the questions have already been answered?
No fair.
Don’t forget the post-awakening Karda Nui, where all life in it was incinerated by the reactivation of the Codrex.
Meh, nobody cares about that one.
In one of the books 9 (can’t remember the name) There was a flash back and Karda nui still had the plants and stuff
im just gonna throw this out there: theres not much unexplaned stuff in bionicle
Tell that to the Makuta.
You know.
The ones who died
Meh, nobody cares about those ones.
Well.
Nobody but the Makuta.
You know.
The ones who died