The Red Line is basically a group of islands connected together.
We know that it has it's own season islands, as explained by Nami
The Red Line that crosses the Grand Line has its own Summer, Winter, Spring and Fall "islands" chapter 604
It is 10,000 meters deep, bears the world capital Mariejois, as stated by Hachi.
The Red Line bears the world capital, Mariejois, and is said to be 10,000 meters deep from ocean level to Fishman Island chapter 496
Due to the same height, it is also considered impassable, all though this has been proven to not be the case as
Besides the sheer height, it is also considered indestructible, as demonstrated by Laboon in chapter 104, as he had been ramming the red line to no avail for a considerable amount of time.