There are a lot of things they learn and find in the giant poneglyph building which actually is a giant fortress. It was used to store important things like documents, books, or great treasures. There are so many things there that the Straw Hats can't explore the whole fortress in just a week.
But they just can't get bored there because there are always new discoveries everywhere they go. The robots estimated that they will need at least 4 months if they want to check everything here with their current pace. That just shows how big this place is and how many things they can find here.
But that doesn't apply for Jon who has shadow clones. He created a lot of shadow clones to check every room in this fortress without the robots' knowledge. They all move stealthily and try to not get discovered by the security system here.
Jon uses this chance to train his infiltration skills because this place has the highest security level of all places he ever visited. He fails many times in the beginning because of how tight the security is here even with his current ninja skills levels that could make him infiltrate any places undetected.
Well, any place other than this place apparently because he failed all his attempts for a whole day. He finally succeeds in the 2nd day and keeps succeeding since then. Then in just a week, he finished checking every room in this fortress, even the garbage dump and ventilation by sending a lot of shadow clones.
The problem is, even though he can check every room, he can't get much information because he can't read anything. He has tried to learn the writing used in poneglyphs from Robin, but it was much harder than he thought and he gave up.
After checking every room, Jon has a lot of free time. So he decides to make new jutsus. He can't read anything inside and can only look at things like a tourist in a museum who doesn't read the tags anyway. So he'd rather do what he can.
The others also do whatever they want here because they can't and don't want to leave yet. It takes them more than 2 years and a lot of life & death situations, so obviously they won't just leave after a week. Besides, there are things they can do here.
Robin is learning everything available here and the others even ask her because she's the only one who can read everything here. She is having the time of her life with all these historical records and ancient knowledge.
Franky is learning the ancient technology to improve the crew's tech. Usopp also learns the ancient weapons and useful knowledge. Chopper is learning the ancient medical knowledge with the reindeer scientist robot.
Nami is learning the ancient navigation system and study about weather that has been translated by Robin. There are some maps too that piqued her interest because there are some locations that aren't drawn in the current age maps she knows.
Brook is hooked with the music from the ancient time that has been recorded and saved in this place. Jane is helping Robin make copies of the records and store them in her inventory. Sanji is glued to recipe books and now trying to recreate some of these recipes.
Meanwhile, the muscle heads can't stay inside the fortress. Jon, Luffy, Zoro, & Jinbe don't have anything to do inside, so they are outside, doing things they like to do. They are exploring the island instead to see if there are other interesting things.
"Hey, Jon, just what are you doing since earlier with your hands while walking?"
"I try to make a new jutsu. I've made the concept and calculated the chakra composition. So now I'm trying to make the hand seals that can knead the correct chakra composition."
"..... Uh, okay. I don't understand, but that sounds cool."
Luffy is still curious, but he doesn't ask anymore because he really can't understand anything. Well, not like Jinbe & Zoro understand either. But they don't really care because now Zoro just wants to find something strong to fight and Jinbe focuses on making sure that Luffy & Zoro don't disappear.
Zoro can suddenly get lost while Luffy can suddenly leave if he sees something interesting. Jinbe's job is being a babysitter now. He thought it would be easier with Jon here, but Jon doesn't help him at all because of the new jutsu research.
They walk around for a whole day but don't really find anything interesting. There's no creature strong enough to threaten them here. In the end, they need to play by themselves like doing personal training or sparring.
A few days later, they find out something surprising. The giant poneglyph fortress actually can fly. It's a flying fortress equipped with weapons of mass destruction and its name is Uranus.
This flying fortress was made after the Ancient Kingdom got destroyed. It was made to defeat the ones that destroyed their Kingdom and conquered the world. Those people were none other than the Celestial Dragons.
But although this fortress was made to defeat Celestial Dragons, it wasn't meant to be used to conquer the world. Its main purpose is to free people from the cruelty of Celestial Dragons. The ancient Kingdom has fought the Kingdoms of those Celestial Dragons for a long time regarding slavery.
After knowing the purpose of this flying fortress, the Straw Hats are speechless. They are amazed by it, but they also feel bad for the people who made this. After all, they have defeated the Celestial Dragons and the new World Government is on the track to abolish slavery from the world.
That's why they understand why this flying fortress was needed. The Celestial Dragons have powerful weapons and people at their disposal. But Jon singlehandedly destroyed everything those Celstial Dragons had before they realized it.
Now this flying fortress has lost its main purpose because the Celestial Dragons have been destroyed. But it also makes them know that the prophecy wasn't 100% correct. Though it was a fact that many of the prophecies have been proved to be right.
"So, what should we do with this fortress now?"
"Should we give it to Luffy's dad?"
"I don't think that's a good idea. It's not that I don't believe in Dragon & Sabo. I truly believe them after spending 2 years with them. But now they are in the World Government and they deal with a lot of people from all over the world. Those people are the ones I'm being worried about. I'm sure some of those greedy Kingdoms will set their eyes to get this fortress and another war will happen."
"Then what should we do?"
"Leave it here for now. Only Luffy can control it anyway, so even if some people somehow manage to find this place, nothing will happen to it. We can think of what to do in the future because I'm sure we will be very busy once we leave this place."
"Ah, you're right."
"What do you mean by being busy?"
"What do you think will happen when people know that we've found One Piece?"
"We will get famous."
"Correct, and they will try to get it from us."
"?! THEY WILL ATTACK US?!"
"Obviously. Not just pirates, even the Marines will go all-out to capture us from now on. While the pirates want the treasures and take the title of Pirate King from us, the Marines want to show their power and inflict fear on the criminals by defeating the Pirate King crew. That situation will last for a rather long time. Maybe a few years."
"H-how are you so sure?"
"Even the Emperors were in such a situation albeit at lower levels. What do you think will happen to the Pirate King crew?"
Color is drained from Usopp's & Chopper's faces as they imagine days of being attacked nonstop by powerful people. They didn't realize that being the Pirate King crew would bring such trouble. But some people here are really anticipating such situations.
"This will be fun."