It is a stretch of Ocean where great treasures, adventures, and romance takes place. It is also said that the Grand line is the most dangerous ocean because of the savage beast, climate, and other powerful individuals including pirates and marines. 

The grand line is covered by the calm belt and the red line which divides the world into four blues (North Blue, South Blue, West Blue, East Blue).

It is divided into two the paradise (first half) and the new world (second half) where the yonkos (emperors) rules the seas.