Newton's idea of Hollow Earth? Isaac Newton's Cenotaph by Étienne-Louis Boullée.

Designed in the late 1700's.
Newton Cenotaph - "Enlightenment Architecture" by Etienne-Louis Boullee
A metaphysical representation of Newton's principle "Order of the Cosmos".

Newton displaced the Earth as the center of the universe, however, his later studies into alchemy and enlightenment led him to more esoteric views that the Earth and Universe are one in the same. In his later years, he was obsessed with finding a portal that would lead him outside the celestial sphere.

Urged by astronomer Edmond Halley (who was studying his now-famous comet), Newton continued to study his notion of gravity and apply it to the motions of the Earth, sun and moon. It all led to his seminal work, published in 1687, called the "Principia" — considered by many as the greatest science book ever written.

The full PDF version is available here:
http://redlightrobber.com/red/links_p...

This model by Boulee was his homage to Newton's enlightenment principles. It is an emblem of the Earth from the Outside and the Universe from the inside.

A paradox of light: When it is daytime outside the sphere, it is nighttime inside the sphere. Whereby the outside's daylight provides the light that illuminates the star's inside. An "inner sun" would create the daytime inside when it was night outside.