Far beneath the center of the earth, there is not molten rock, but… a civilization? Highly evolved super-beings? Mole-people? There are a lot of sci-fi stories that like to explore this idea. After all, it wasn’t until recently that we knew there was something other than dirt down there, and even then, we haven’t been able to actually send a human very far beneath the surface. Though we have learned a lot more about the earth’s core, there’s still a lot of mystery surrounding it.
Why this is bad: If you’re trying to have a very science-based story, you might have a hard time with your readers here. Suspension of disbelief can only go so far, and because of the advancement of technology and scientific knowledge, it’s going to be a lot harder for readers to accept that aspect of your story’s world. If you have a lot of other unbelievable things in your novel and it isn’t based around any mythology, you’ll probably have an issue immersing readers in the world.
What you can do to fix it: Figure out what you’re willing to compromise on. If you’re going to have a modern day story with a hollow earth, you’re not going to have a lot of wiggle room when it comes to stretching the imagination.However, if your story has a more ancient, fantastical setting, your readers are probably going to find it easier to swallow. When it comes to these types of locations, readers find it easier to be forgiving. Even still, it’s going to be difficult. If you’re going with this trope, think carefully about what you really need to push and be aware of how much your reader is willing to accept before they can no longer feel part of your story’s world.
Bottom Line: Suspension of disbelief can only go so far, and a hollow earth requires a lot. If you have this, you’re going to need to be more realistic with the other aspects of your world, so keep that in mind.