Stonehenge

"Swindapa's lineage, the Kurlelo, lived by the Great Wisdom - Stonehenge - far south of here in Wiltshire on the open upland downs. By Fiernan reckoning, that made them the center of the world; the Kurlelo Grandmothers were the high priestesses of Moon Woman and students of the stars that revealed Her will. Those dry and sunny hills were thickly peopled and closely farmed as well..."
-SM Stirling, On The Oceans Of Eternity (New York, 2000), Chapter One, p. 16.

"The world" can mean the universe, the planet or society. In the third sense, where is the center? Rome? London? New York? The Great Wisdom? It depends when we are.

Stonehenge is:

built by a time traveler in Poul Anderson's The Corridors Of Time;
the center of the world to one section of ancient society, as Babylon is to another, in Stirling's Nantucket Trilogy;
visited by an immortal in Anderson's The Boat Of A Million Years;
duplicated by a playful protector in Larry Niven's Protector.

For some Anderson references, see here.