Location from One Piece by Eiichiro Oda
A continent-sized wall of red rock circling the entire globe perpendicular to the Grand Line, dividing the world's oceans. The Holy Land Mary Geoise sits atop its summit.
The Red Line is the world's great divider. It intersects the Grand Line at two points: Reverse Mountain (where the first half begins) and Mary Geoise (where Fish-Man Island lies far below the waterline). To cross it, ships must either ride the bizarre upward currents of Reverse Mountain or be coated in resin to dive 10,000 meters to Fish-Man Island and pass beneath. The World Government chose the summit of this impassable barrier as their seat of power — symbolism that isn't lost on anyone. Some theorize the Red Line is not natural at all, that it was created during the Void Century. If the ancient prophecies are true, someone will eventually destroy it, reuniting All Blue and freeing Fish-Man Island.
An impossibly vast cliff face of dark red stone rising thousands of meters from the ocean surface, stretching endlessly in both directions until it curves beyond sight. Its sheer walls are unclimbable, stained by millennia of salt spray. At its summit, the white spires and golden domes of Mary Geoise gleam in the sunlight, visible only to those who know to look up. The Red Line is less a landmark than a geological impossibility — a wall that splits the entire world in two.
Also known as: Red Line, The Red Continent