I think that it is obvious. Minas Tirith is based on Athens, Osgiliath is Istambul, Argonath are the Iron Gates on Danube, Rohan is Poland(famous Polish cavalry plus the name "rohan"=>"roh" in all slavic languages means "horn", Misty Mountains are Carpathians and White Mountains(they are even both arches) are Balkan Mts. The Shire is England and the Mordor is in Eastern Turkey(surrounded by Caucasus Mts.). Helm's Deep is totaly based on Predjama Castle, Edoras on Spiš Castle. They are two of the most iconic and extraordinary castles in europe, one is built into a mountain, the other is built atop a hill on the foot of rocky Carpathians. Edoras could be possibly some of british castles, but I don't know about anyone that maches the description or one of Swiss/German/Austrian Alpine castles, like Hohenwerfen castle.