Erebor - The city of the Dwarves under the Lonely Mountain.

"'Oh very well,' said Thorin.  'Long ago in my grandfather Thror's time our family was driven out of the far North, and came back with all their wealth and their tools to this Mountain on the map.  It had been discovered by my far ancestor, Thrain the Old, but now they mined and they tunneled and they made huger halls and greater workshops - and in addition I believe they found a good deal of gold and a great many jewels too.  Anyway they grew immensely rich and famous, and my grandfather was king under the Mountain again..." ~The Hobbit, chap. I (An Unexpected Party)