The latter half of the Grand Line, the New World.
Near the waters of Wano Country, heavy clouds blotted out the sky, fierce winds howled without end, swift currents and whirlpools surrounded the area, and reefs littered the seafloor below.
If one's sailing skills were lacking, or if they were unfamiliar with the underwater terrain nearby, a single misstep could lead to shipwreck and death.
Upon the towering rocky shores stood watchtowers and gun batteries, manned by Beast Pirates sentries who remained constantly alert to their surroundings...
If an unidentified vessel suddenly approached, they would sound the alarm and open fire to sink it.
Even if a powerful fighter aboard an invading ship could withstand the cannon fire launched from the rocky shores, the vessel would face another enormous problem once it ventured deeper inside...
Wano Country was surrounded by a towering wall of rock. On all sides were waterfalls hundreds of meters high, with torrents roaring downward.
Under normal circumstances, invading ships had only two ways to climb the rocky wall.
The first was to tie ropes around the enormous carp that occasionally appeared and swam upstream, letting them pull the ship upward.
The second was to abandon the ship and climb the hundreds-of-meters-high rocky wall by hand.
However...
Once you climbed the wall, you would despair to discover that above it lay another dangerous stretch of waters, with equally treacherous terrain and swift currents.
Even worse, the rocky shores there were still equipped with gun batteries guarded by sentries...
However, it was much simpler for Beast Pirates ships to enter Wano Country. They would neither be shelled by the sentries nor need to painstakingly climb the rocky wall.
Beneath the waterfalls, the rocky wall had special mechanisms and passageways that could directly transport ships from the waters below