Voyage to Our Hollow Earth!
http://www.ourhollowearth.com/VoyagetoHollowEarth.htm

History of the Hollow Earth Theory
http://tlonh.com/articles/hollowEarthHistory.asp

Hollow Earth by Angus Sutherland
http://www.ufoarea.com/main_hollow.html

Hollow Earth Expedition: Brooks Agnew Pt.1
http://www.youtube.com/watch?v=M70JhlnRmpM