Many readers of the paranormal and the unexplained are familiar with the theory that the Earth is hollow. The idea is based on the ancient legends of many cultures that say there are races of people — entire civilizations — that thrive in subterranean cities. Very often, these dwellers of the world beneath are more technologically advanced than we on the surface. Some even believe that UFOs are not from other planets but are manufactured by strange beings in the interior of the Earth.

Who are these strange races of beings? How did they come to live inside the Earth? And where are the entrances to their underground cities?

Agartha (sometimes Agartta, Agharti or Agarttha) is a legendary city that is said to reside in the Earth's core. It is related to the Hollow Earth theory and is a popular subject in Esotericism. Agartha is one of the most common names cited for the society of underground dwellers. Shamballa (also known as Shambalah or Shangri-La) is sometimes said to be its capital city.

The mythical paradise of Shamballa is known under many different names: It has been called the Forbidden Land, the Land of White Waters, the Land of Radiant Spirits, the Land of Living Fire, the Land of the Living Gods and the Land of Wonders. Hindus have known it as Aryavartha (literally : The Land or Realm of The Aryans ; the Land of the Noble/Worthy Ones") - the land from which the Vedas come; the Chinese as Hsi Tien, the Western Paradise of Hsi Wang Mu, the Royal Mother of the West; the Russian Old Believers, a nineteenth-century Christian sect, knew it as Belovodye and the Kirghiz people as Janaidar. But throughout Asia it is best known by its Sanskrit name, Shambhala, meaning 'the place of peace, of tranquillity.'

The entrances. There are allegedly several entrances to the Kingdom of Agharta throughout the world:

• Kentucky Mommoth Cave, in south-central Kentucky, US.
• Mount Shasta, California, US - the Agharthean city of Telos allegedly exists within and beneath this mountain.
• Manaus, Brazil.
• Mato Grosso, Brazil - the city of Posid supposedly lies beneath this plain.
• Iguaçú Falls, border or Brazil and Argentina.
• Mount Epomeo, Italy.
• Himalayan Mountains, Tibet - the entrance to the underground city of Shonshe is allegedly guarded by Hindu monks.
• Mongolia - the underground city of Shingwa allegedly exists beneath the border of Mongolia and China.
• Rama, India - beneath this surface city is a long lost subterranean city, they say, also named Rama.
• Pyramid of Giza, Egypt.
• King Solomon's Mines.
• Dero Caves, ?.
• North and South Poles.