https://www.looper.com/1663066/lord-of-the-rings-unseen-world-rings-of-power-explained/

Amazon's "Rings of Power" (https://screenrant.com/db/tv-show/the-lord-of-the-rings-the-rings-of-power/) just made a reference to Tolkien's Unseen world - here's everything you need to know about the "other side."