I'm new here and this is my first question.
I have a question which is a bit complicated about an idea that I like but that is confusing me at the moment. I appreciate if you bear with me and it would mean so much to receive your feedback.
I'm going to elaborate a bit about this question, so hopefully, you get a better idea. There is a world, inside our earth, but it cannot be seen by humans - it is as if it isn't there for us. This inner world is both located and the same size as the inner part of our earth. At the same time, this hidden space is not affecting our earth in other ways (gravity, temperature etc.), because it only has the same space of our inner world, which is hidden. This earth is completely different than what our inner world looks like - it's like another world with different physical laws etc. Humans can access it through portals from above. Through these portals then they can be teleported into this 'other world' inside our world (earth) - not by physically going there (i.e. drilling the earth or burrowing etc.) but through magic (portals). This world becomes real to us and starts effecting us only when it cracks through the surface if it expands; when it comes in contact with the surface of the earth (this is a very important aspect). This is like a world inside 'hollow earth', but with different geology (for example, there are no earth layers that we know of) and it exists like an invisible hidden space within our world that can be accessed by portals from above.
I know that it is a bit complicated because for me it seems that I have some kind of portal/parallel world hybrid in my mind. Maybe there is something else (a theory, a story, a question posted before this one that I haven't read, etc.) that is close to what I'm envisioning and that it can help me with world-building or researching similar ideas. Maybe it has been done! I'd like to add that I'm still in the early development of this world, if it can, after all, work.
I would appreciate if you let me know about anything you think might help me and would be very happy to answer your questions to clear some things up. Thank you for taking the time to read this and any feedback, criticism, thoughts etc. would be extremely appreciated!