Europe is a peninsula that makes up the western fifth of the Eurasian landmass. Its maritime borders are made up of the Arctic Ocean to the north, the Atlantic Ocean to the west, and the Mediterranean, Black, and Caspian Seas to the south Land relief in Europe shows great variation within relatively small areas. The southern regions are more mountainous, while moving north the terrain descends from the high Alps, Pyrenees, and Carpathians, through hilly uplands, into broad, low northern plains, which are vast in the east. This extended lowland is known as the Great European Plain, and at its heart lies the North German Plain. An arc of uplands also exists along the north-western seaboard, which begins in the western parts of the islands of Britain and Ireland, and then continues along the mountainous, fjord-cut spine of Norway.