This isn't 'entirely' focused on the hollow earth, but some of the underground cities I will refer to may very well have connections to the hollow interior of the planet.
I will simply repost this message that I sent to another group. If there is an underground city that has the most EVIDENCE of its existence, it is probably the one beneath Death Valley and the adjacent Panamint mountains of California. If anyone has info that they can ADD to this collection of evidence, please do share it with us.
Here is the post:
I will not go into great detail concerning the following links, I will just let the "links" and the revelations within them speak for themselves...
Ancient astronauts in California who colonized other star systems FROM EARTH...from their massive underground cavern cities beneath Death Valley's Panamint mountains:
https://www.bibliotecapleyades.net/vida_alien/alien_races03a.htm
Two men who claim to have explored the upper levels of an abandoned underground city beneath the Panamint mountains. The city was vacant, suggesting that its inhabitants migrated to even deeper cavern systems below:
http://www.subterraneanbases.com/ancient-civilization-beneath-death-valley/ & http://www.angelfire.com/ut/branton/10466.html
Brazilian UFO "contactee" is taken to a huge underground base-network beneath Death Valley by visitors from the Vega star system:
https://www.bibliotecapleyades.net/vida_alien/warheaven03.htm
Tom Wilson, a Paiute 'Indian' talks about the discovery of an underground 'city' beneath the Panamint/Death-Valley area:
Even the convicted murderer Charles Manson claims to have heard of this underground 'world' beneath Death Valley:
http://murdersofaugust69.freeforums.net/thread/483/charles-manson-search-underground-world
More on the colonization of other worlds using the ancient technology of those ancient sea-faring surface dwellers who took refuge within the underground cities of the Panamint/Death-Valley regions:
http://www.angelfire.com/ut/branton/erthbrn1.html
Lost underground City of the Death Valley Desert Giants:
%22Lost City of the Desert Giants%22 %22Death Valley%22 - Google Search
Advanced human civilization Under the California Desert (in Spanish):
https://www.youtube.com/watch?time_continue=86&v=Zzsanw3gtyQ
Two weird trips to Death Valley... 1849 and 1949. Giants, aliens, underground cities of gold:
https://beta.prx.org/stories/267590
http://www.google.com video search for: Death Valley - Panamint - underground city:
%22Death Valley%22 Panamint %22underground city%22 - Google Search
http://www.google.com video search for: Death Valley - underground - giants:
%22Death Valley%22 underground giants - Google Search
http://www.google.com video search for: Death Valley - underground - aliens:
%22Death Valley%22 underground aliens - Google Search
http://www.google.com video search for: Death Valley - Panamint - underground base
%22Death Valley%22 Panamint %22underground base%22 - Google Search
http://www.google.com video search for: Panamint subterranean:
Panamint subterranean - Google Search
branton