This link goes deeper as it covers a lot including:
Aghartha In The Hollow Earth!
By Dr Joshua David Stone
The Channelings of Djwhal Khul on the Hollow Earth
Admiral Richard B. Byrd's Diary (February - March 1947)
The exploration flight over the North Pole
The Inner Earth - My Secret Diary
Traveler to the Inner Earth
The Realm of Aghartha as described by the Members of the Galactic Federation Council of Sirius – 7 February 2006 [Through Sheldan Nidle]
THE SMOKY GOD or A Voyage to the Inner World
by WILLIS GEORGE EMERSON - 1908
OLAF JANSEN'S STORY
MY name is Olaf Jansen. I am a Norwegian, although I was born in the little seafaring Russian town of Uleaborg, on the Eastern coast of the Gulf of Bothnia, the Northern arm of the Baltic Sea.
Our Oceans and Beaches - Our Water is Alive with Consciousness
Good morning. It is Mikos calling to you from the ocean shore in the Hollow Earth, where I am walking along the beach watching the waves lap the sand. Our oceans are large, nay huge in comparison to yours, with waves larger in size and stronger in force. The oceans flow swiftly around our inner globe, and ebb and flow in tides affected by the Earth's outer Moon just as your tides are. For the magnetic pull of the Moon is felt inside the Earth as well.
Adama of Telos talks of his experience of visiting the Oceans and Mountains within the Inner Earth cavity
“TELOS - A Subterranean City beneath Mt. Shasta” - Dianne Robbins.