the theory seems absurd at first glance, like the theory about a spherical earth seemed to people in the 15th century. At further inspection there is much to it.
Consider how easy it could be disproved: Take a few snapshots off a satellite that is near each pole (or hole, for that matter), and let those snapshots clearly show the icecaps on the poles without cloud-cover. 
This should be as easy as - say - taking snapshozs from the stars when on the moon (the equipment for that purpose would weigh considerably less than a totally unnecessary moonrover, which they took purportedly to the moon), such pictures would have proven once and for all the authenticity of the manned moon-landings, for they could not have been faked on earth - but that is another story.
Anyway, until proven wrong by said photographs I will adher to this theory.

contents:

folders:
1829 Olaf Jansen - the smoky god
1896 ETIDORHPA
1897-Nansen-FarthestNorth
1906 William Reed - THE PHANTOM OF THE POLES
1920 Marshall B. Gardner - A Journey to the Earth's Interior
David Standish - Hollow Earth (mobi + epub)
disappearance of the Greenland-Vikings
hollow earth - photos
hollow planets - photos
large freshwater lakes beneath antarctic ice
location of openings
The Underworld Empire

files:
1513 piri reis map.pdf
1845 Louis Holberg - Niels Klim's journey under the ground.pdf
1993 Interview mit Frank E. Stranges.pdf
2008 coloured antarctic icebergs.pdf
2010 antarctica-mysteries.pdf
2010 evidence removed from google earth.pdf
antarctic bases and ufos.pdf
antarctic map 2.pdf
antarctic map 3.pdf
AntarcticAurora123.pdf
Apache_Underground.pdf
Curvature_Anomalies.pdf
Death Valley.pdf
Frobisher.pdf
Geophysical facts about the Hollow Earth.pdf
HinduKush.pdf
History of The Hollow Earth Theory.pdf
Hollow Planet Seismology Vs Solid Earth Seismology.pdf
Icebergs.pdf
jan_lamprecht_-_hollow_planets.pdf
Japanese_Caverns_Worlds.pdf
Massive 'Ocean' Discovered Towards Earth's Core.pdf
Mt. Moncayo.pdf
Mysterious Places Around The World 1.pdf
Mysterious Places Around The World 2.pdf
Mysterious Places Around The World 3.pdf
operation highjump 1947.pdf
polar mystery.pdf
Polar Warming.pdf
Radarsat.pdf
Ring.pdf
THE FLIGHT TO THE LAND BEYOND THE NORTH POLE.pdf
The Subterranean World of the Macuxies.pdf
UnderGround Brazil.pdf
United States Patent 1096102 - The Hollow Earth Theory.pdf
World Top Secret - Our Earth Is Hollow !!!