The Holy Land of Mariejois, the capital of the World Government. In a magnificent castle, the Gorousei meet. World Nobles also call the grandiose home. Mariejois is the only entrance to BOTH the Grand Line and the New World.
Reverse Mountain, where the four Seas meet and flow to the Grand Line. Precipitous and deadly, Reverse Mountain is the pirate's most common means of entering the Grand Line. A skilled navigator is essential to passing through unharmed.