Mobile, currently located in the Blue Area of the Moon; formerly located in the northern Atlantic Ocean and in the Himalayas
Attilan is far more technologically advanced than other cities of its era. The Inhumans have used their technology to relocate the city and the island upon which it is built to other locations, even taking it off of the planet itself.
Fantastic Four #47
Attilan is the ancestral home of the Inhumans, a highly advanced offshoot of the human race. About seven thousand years ago, the Inhumans grew tired of centuries of persecution by their more primitive parent race, and decided to create a place of refuge for themselves. Under the leadership of King Myran, the Inhumans chose as a site for their city a small island in the northern Atlantic Ocean, located about two hundred miles southwest of Iceland. The city, which took several decades to complete, was named Attilan, a name derived from Atlantis, the former pinnacle of civilization on Earth that had vanished beneath the sea about three millennia before. Attilan has been the sole center of the Inhuman population ever since.
For millennia, the Inhumans dwelled in Attilan, isolated from contact with mainstream humanity except for an occasional encounter with a lost Greek or Viking sailing vessel. Finally, in the mid-Twentieth Century, with the advent of steamships and airplanes, the Inhumans began to fear discovery by the human race. When one of his subjects was captured by human beings, young king Black Bolt determined that the Inhumans must move their civilization to some place more secure. Employing anti-gravity generators, the Inhumans moved their entire city and its foundation in one piece. The new site of Attilan, a hidden valley in the Himalayan Mountain range in China, was excavated by the Eternals, another variant offshoot of humanity. The Himalayan site of Attilan became known as "the Great Refuge." The Himalayas did not prove to be remote enough to enable the Inhumans to retain their secrecy, however, and soon the Inhumans' existence became known to several of the governments of the outside world, although not to the general public. While in the Himalayas, all of Attilan's ancient architecture was accidentally destroyed by Black Bolt and the city has been extensively redesigned and rebuilt.
Attilan was relocated once again, this time to escape the effects of Earthly pollution and disease. Attilan is currently located in the "Blue Area of the Moon," nestled in the ruins of an ancient city built by the alien Kree whose technology gives the "Blue Area" its own artificially created atmosphere.