Documentary on Hollow Earth

Here is a YouTube video of a very well done documentary of Hollow Earth.  It is a three part series.  The last video you can go 1/3 into it as it repeats the last half of part two.  While I am not saying I subscribe to this theory, I am reminded that at one time, people thought the world was flat.  Science now shows we have a changing facts as we know them about our world and universe.

Part One:  http://www.youtube.com/watch?v=uEhc17CKnmk&feature=youtu.be

Part Two: http://www.youtube.com/watch?v=nvNoy6nYVSU&feature=related

Part Three: http://www.youtube.com/watch?v=iQ9uose9R7U&feature=related

There are many videos on youtube about hollow earth but I find these the most informative – I am left pondering this issue.