there is no credible scientific evidence to support the existence of a fully developed world or civilization underneath Earth's crust. The Earth's crust is a relatively thin layer compared to the overall size of our planet, and it is where we find the solid ground on which we live.
Beneath the Earth's crust lies the mantle, a semi-solid layer composed of hot, flowing rock, and beneath that is the Earth's core, made up of a solid inner core and a liquid outer core primarily composed of iron and nickel.
The idea of a hidden world or civilization underneath the Earth's crust is a common theme in mythology, folklore, and some works of fiction. However, these are purely speculative and imaginative concepts and do not have any scientific basis.
It's important to distinguish between scientific knowledge supported by evidence and speculation or fiction. As our understanding of the Earth and its internal structure continues to advance, scientists may discover new insights about the planet's interior, but for now, there is no evidence to suggest a hidden world exists beneath the Earth's crust.