Hey there, I was hoping that this is the place to post this. (And I apologize in the first place if this has been posted/discussed already)
If you look at the bottom panel you can see a globe of the OP world with 6 Moons orbiting around it, and one of the moons (the middle right one) has its own moon.
Now, as we all know, Enel went to the moon in his Maxim Ark (which of these moons did he went to, from this pic it looks like a rather plain moon, which in my view, is most similar to the middle top moon in the globe on the manga; it could also be the middle right one, but in the cover page there was no indication of a second moon)
Whatever the moon, it's really unimportant, what matters is that this cover story has revealed two things: the existence of life in space in OP, here and here (in the second pic, you can see the space pirate bleeding from Enel's kick, so the space pirates are not robots like these little guys: pic
But, more relevant to this thread, the fact that there is this: Pic 1, Pic 2, Pic 3
An ancient underground city in the moon (the middle top one, in my opinion)
So, according to Enel's cover story, there's an ancient city (Birka) on one of those moons, that city seems to have advanced technology, and the people who lived there seem to have been the ancestors of the Skypeans and Shandians.
I'm wondering if there are other ruins on the remaining 5/6 moons; also I think Oda said in an early SBS to "pay attention to the moons" or something similar (I'll try to look for it and post a link here) So, at least the moon Enel went to, should be important to the main story in the future, do you guys think we will ever see the strawhats have some sort of space adventure? And get to see the moon(s) in more detail?
(I'm not sure if moons fall in the "geography" category, but seeing as there isn't an "One Piece astronomy" thread, I thought I'd post this here)