So, we have a giant straw hat in Mary Geosie and we can see seven chambers.
Now for the speculation. In every chamber there is a straw hat, for each race in the One Piece World.
The Ancient Kingdom had seven rulers and one of them was Joy Boy.
The straw hats were the symbol of the Ancient Kingdom and stands for a free and united world.
1. Humans – this chamber is empty.
(Straw Hat -> Joy Boy -> ??? -> Gol D. Roger -> Shanks -> Luffy)
2. Giants – The straw hat we saw in chapter 906 / episode 885
(We don’t know much about the Long-Tribe. There are theories, that the arm- leg- and necktribe were all the same in the past. An all-long-tribe. I don’t know if this is true, but if, then the mysterious guy could be one of them)
Except for the Skypieans and Humans, these races are in the slave list.
Except for the Humans everyone of these races lives hidden:
Fishmen – under water
Minks – constantly hiking Zou
Skypiea – hidden in Sky Islands
Tottanas – under earth
Giants – isolated in the mighty Elbaf
Long-tribe – ???
It would be cool, if the Ancient Kingdom consists of those rulers. Everyone had their own straw hat. The giants a large one and the tontattas a very small one.
On the cover page with Enel you can see the three Ancient Weapons. You can see Sea Kings (Poseidon), a ship (Pluton) and the sun (Uranus)
Uranus – Why the sun?
At Fishman Island King Neptune tells the Straw Hats that there is a mighty tree named “Sunlight Tree Eve” which transfers light from the surface straight down to the ocean floor with his colossal roots. It’s a holy and mysterious tree, absorbs light and supply air to the ocean floor.
This is the reason why Fishman Island is located at this place.
Even the Fishman Pirates call themselves Sun Pirates and have the sun as symbol.
Usopp stated that there might be a connection to the Treasure Tree Adam (Adam and Eve? No coincidence!)
What is on the surface?