Under the crust is the mantle, the largest of the Earth's different layers, filled to the brim with warm red rock. When it breaks upwards through the surface, dramatic volcanic eruptions occur, as so often, new crust is formed as it cools.
In the heart of the planet, there is the core of the Earth, divided between the outer and the inner. Some Indian tribes tell stories of life, of their ancestors who came from caves to populate the surface.
Perhaps the most important is that the hollow Earth theory was propagated by the astronomer Edmond Halley - as in Halley's comet.
The idea of "Hollow Earth" was brought to life and made exciting by the science fiction author Jules Verne, who wrote the novel "Journey to the Center of the Earth" in 1864.
The characters travel in an underground world full of prehistoric flora and fauna. Digging dinosaurs are a relatively new discovery for paleontologists.
Still, it is believed that some prehistoric creatures may have dug into the Earth's crust to escape their extinction sixty-six million years ago.
These particular dinosaurs did not survive and were killed along with most others. Still, if the Earth was empty, they would have dug in another place, with a chance of survival.
Thanks to the probably warmer climate within a planet, there might finally be a place for the infamous reptile humanoids of various conspiracy theories.
Otherwise, if Earth's emptiness were a discovery that was made only recently and was not always known, normal humans would undoubtedly operate spaceships to and from this Middle Earth to make the most of it.
We know this through the efforts of the real world to penetrate the real Earth. We have been drilling on our planet for centuries, mainly to extract fossil fuels - although speleology is also a leisure activity and people have traveled to incredibly deep places.
What would happen if you drilled into the earth's core?
The deepest cave discovered to date, Veryovkina Cave in Georgia, reaches 1.37 miles below the surface. Unlike small arthropods that live naturally at these depths, humans are not built for caving.
We cannot squeeze through all the cracks to see how deep a cave is. And those 1.37 miles in Georgia are nothing compared to the actual diameter of the planet, which is more than 7,900 miles in the center.
However, the deepest hole that man has ever drilled is much deeper than the Veryovkina cave. The Kola drill in Russia stretches over 7.5 miles, deeper than the Challenger Deep at the bottom of the Mariana Trench, the ocean's deepest point.
If Hollow Earth still had a molten mantle beyond its boiling point, any passage through it would have to be made of a material like a solid diamond, whose melting point could withstand many thousands of degrees Fahrenheit. The temperature of the Earth's interior at the boundary between the mantle and the outer core is estimated at more than 6,500 degrees. This planet's structure would be completely different without magma, convection currents, or plate tectonics.
There would be no magnetosphere, no atmosphere, no life. It will always be just a science fiction dream and not an everyday reality as exciting as the idea is.