Most people have made this mistake of thinking Middle-earth is a particular kind of earth or is another planet of the science fiction sort but it's just an old fashioned word for this world we live in, as imagined surrounded by the Ocean.
J. R. R. TolkienStand by the grey stone when the thrush knocks, and the setting sun with the last light of Durinโs Day will shine upon the key-hole.
J. R. R. TolkienThe wide world is all about you: you can fence yourselves in, but you cannot for ever fence it out.
J. R. R. TolkienGandalf! I thought you were dead! But then I thought I was dead myself. Is everything sad going to come untrue? What's happened to the world?" A great Shadow has departed," said Gandalf, and then he laughed and the sound was like music, or like water in a parched land; and as he listened the thought came to Sam that he had not heard laughter, the pure sound of merriment, for days upon days without count.
J. R. R. Tolkien