It must be the Mediterranean, surely - median, meaning situated in the middle, terrestrial, meaning of or on or relating to the earth....
terra
The name Mediterranean sea comes from mdei meaning middle and terra meaning earth, so it literally means middle earth sea.
Ask the sea in the middle of the earth
The sea to the West of Middle Earth is Belegaer. It means Sundering Sea in High Elvish. Across it to the West lie the Undying Lands that Frodo, Bilbo and Gandalf and all the others sail to at the end.
Mediterranean Sea
the Atlantic sea
Mediterranean Sea
the Mediterranean sea
Mediterranean Sea
The most western sea is the Sundering Seas (aka Belegaer or The Great Sea) that separated Middle-earth from Valinor.
The correct spelling is Mediterranean Sea, containing terra (it means "middle of the Earth").
Mediterranean Sea