Translated from Kitaro no Tengoku to Jigoku
There are many different legends about what is called the Root Country (Ne no Kuni), and no one really knows for sure what the original concept was.
According to one story, the Root Country is the deepest part of an underground land, that is to say the roots of the Earth. This gives it the name Root Country. Another legend says that the Root Country is the source of all vegetables and all food harvested from the soil, and that is where the name comes from.
In the Kojiki, the Record of Ancient Matters, there is a myth that records the Emperor’s visit to the Root Country, where everything was much the same as the above-ground world including a great palace. This palace was the home of Susanoo, one of the major deities of Shinto.
百物語怪談会 Hyakumonogatari Kaidankai 
Jul 21, 2013 @ 17:11:40
this reminds me of the “Hollowed Earth” legend.