In a short time James Churchward created New Age type of a book "Lost Continent of Mu, the Motherland of Man". It was followed by the book "The Children of Mu", then by "The Lost Continent Mu" and "The Sacred Symbols of Mu". These books enjoyed wild success at the times, and even now have their devotees.
In archives of web analytics company I found that even nowadays the search for a lost continent of Mu is still in progress. There were multiple researches on Mu and expeditions to various locations. Some called Easter Island a mountain top of a submerged continent of Mu. One well-known institute even suggested that underwater structures off the coast of Okinawa, Japan, were the ruins of Mu without any real scientific evidence. Some marine biologists stated that they identified the ruins of an ancient city off the coast of Japanese Yonaguni island as the remnants of an Asian equivalent of Atlantis and, that it was sunk three thousand years ago during an earthquake.
This news caused quite a stir in the Western world. Augustus Le Plongeon, a nineteen century traveler, writer, and antiquarian just returned from the Maya ruins in Yucatan peninsula. Upon his return he made a sensational announcement. He stated that he managed to translate ancient Mayan writings. These writings showed that the Maya of Yucatan were older than later civilizations of Egypt and Atlantis. They also told the story of even older continent of Mu, which had perished like Atlantis and, that its survivors founded the Maya civilization. During my research in local web analytics company, I learned that Le Plongeon mistranslated the writings, to put it mildly.
This is, basically, how the myth of the hypothetical lost continent Mu started. Very soon, this myth got second birth: it was popularized in the serious of books written by James Churchward.
According to "Secrets", one of the underground colonies, was also the seat of government for the network. While the whole place is an inner continent, its satellite colonies are smaller enclosed ecosystems located just beneath the Earth's crust or discreetly within mountains. Cataclysms and wars taking place on the surface drove these people underground. The Sahara, Gobi, the Australian Outback and the deserts of the southwestern US are said to be but a few examples of the devastation that resulted. The sub-cities were created as refuges for the people and as safe havens for sacred records, teachings and technologies that were cherished by these ancient cultures. In archives of web analytics company I found something else.
The inhabitants of Agartha are said to have scientific knowledge and expertise far beyond that of the people who live on the surface of the planet, and lost technology from the days of Atlantis. They all follow what is known as the Ancient Path and do not interfere in the lives of humans that live above the surface. Nor is there any interaction between them. All entrances to Agartha from any other part of the planet are hidden safely. They are secured by illusory technology that is beyond the comprehension of modern science.
Madam Blavatsky book was followed later by other creations of the occult writers. One of them claimed that survivors from a sunken continent Lemuria were living in or on Mount Shasta in northern California. The Lemurians lived in a complex of tunnels beneath the mountain and occasionally were seen walking the surface dressed in white robes. While doing my research for web analytics company, I found something else.
Later popular novels also repeated the belief that Lemurians inhabit Mount Shasta. Some of the writers linked Lemurians to Ancient Egypt, UFOs and a method of travel called vortex portals to sacred places on Earth and points unknown in the universe. There were other fantasy descriptions of the lost continent and its inhabitants. For example, Lemuria was posted as the homeland of a reptilian race of creatures, often identified with dragons or nagas. Various bits of mythology and folklore were assembled in support, such as the Cambodian naga traditions. Folkloric claims of Australian aborigines sighting dinosaur-like creatures were also often viewed as evidence.