Agartha (Agharta) is the name given to the imaginary world believed by some to exist inside the Earth and now incorporated into a number of the Hollow Earth ‘theories’(a).In fact Agartha or as he called it ‘Asgartha’ was invented by Louis Jacolliot (1837-1890).
One site offers video clips to support the Hollow Earth idea(e).
In 2001, a father and son team, Kevin & Matthew Taylor, combined the hollow earth theory with the idea of an expanding earth in their book, The Land of No Horizon. They also have a promotional website(c) as well as a YouTube clip(f).
A number of 20th century writers have suggested that subterranean Agartha has a civilisation related to that of Atlantis. We should not be surprised by the existence of Hollow Earth theories, after all, the Flat Earth Society(b) is alive and well and functional in California*(see Eric Dubay). An international Flat Earth conference in November 2017 was reportedly sold out(g).*
It seems that no matter how daft the idea, followers are always available.
One website(d) describes our hollow earth as the home of the lost tribes of Israel which they defend with flying saucers.
(c) http://www.hollowearththeory.com/ (link broken 19/06/1)
(e) http://thetruthbehindthescenes.wordpress.com/the-hollow-earth-theory/ (offline Oct. 2016)