Wano Country, in the snow-covered Ringo region.
Off a remote stretch of coast, five hundred meters beneath the sea, members of the Flying Pirates discovered a mysterious cavern.
Caverns like this were hardly uncommon beneath the sea.
Ever since the Flying Pirates had settled in Wano Country, they had collected the riches from selling seastone without interfering in the struggle between the Overlord Dragon Pirates and the Silver Axe Pirates.
During that time, violent clashes had erupted between the two pirate crews more than once.
Meanwhile, the two Great Pirates, "Overlord Dragon" Zack and Silver Axe, had fought several major battles themselves.
None had ended with a decisive victor.
There was no stopping such things.
As far as the other factions were concerned, all that mattered was that their substantial profits from seastone remained unaffected.
The members of the Flying Pirates, however, had been searching Wano Country for something under orders from "Uranus" Reinhardt.
They had already searched all the land, finding no unusual places where a massive object could be hidden.
But the sea level had risen several times over the past eight hundred years.
The entrance to wherever that massive object was hidden could very well lie in the sea, beneath its surface.
After countless hardships, they had searched more than half of Wano Country's coastline.
Now, at last, they saw a glimmer of hope.
Underwater caves were actually a very common sight.
But this time was different.
This was the first time they had found a cavern that went so deep.
The caves they had found before were merely holes whose ends could be seen at a glance.
They kept pushing deeper, then began swimming upward.
Suddenly, they broke the surface and breathed air.
There was an enormous space inside the cavern,
but hardly anywhere to stand.