Agartha (sometimes Agartta, Agharti, Agarath, Agarta or Agarttha) is a legendary kingdom that is said to be located in the Earth's core. It is related to the belief in a hollow Earth and is a popular subject in esotericism.
In his 1922 book Beasts, Men and Gods, explorer Ferdynand Ossendowski relates a story which was imparted to him concerning a subterranean kingdom which exists inside the Earth. This kingdom was known to a fictional Buddhists society as Agharti.
Agartha is frequently associated or confused with Shambhala which figures prominently in Vajrayana Buddhism and Tibetan Kalachakra teachings and revived in the West by Madame Blavatsky and the Theosophical Society. Theosophists in particular regard Agarthi as a vast complex of caves underneath Tibet inhabited by demi-gods, called asuras. Helena and Nicholas Roerich, whose teachings closely parallel theosophy, see Shambhala's existence as both spiritual and physical.