The continent of Middle-earth was shaped in the most ancient days of Arda. It lay to the east of the other great continent of Aman (Undying Lands), and was separated from Middle-earth by the Great Sea Belegaer.
At the end of the Third Age, the continent of Aman finally departs from Arda, leaving the mortal realm of Middle-earth which would eventually evolve into Europe, Asia, Africa and Australia.
Places
Shire · Bree · Rivendell · Moria · Lothlórien · Fangorn · Isengard · Mirkwood · Grey Havens · Blue Mountains · Misty Mountains · Trollshaws · Anduin Vale