Human Realm is one of the three known realms in the God of High School world. It is mainly populated by humans and is identical to our known world. In terms of how powerful it is, it is the lowest followed by the Sage Realm and then the Heavenly Realm at the highest.
Humans used to borrow the power of Gods to fight against Demons. The system of borrowing is then destroyed by Hwanung, leading to the Gods placing taboo, a restriction, on humans. The taboo prevent humans from attacking Gods.
Later, with the power of The Key, human can unlock this taboo, making them able to attack Gods. Ultio R later managed to completely destroy this taboo system, leading to human finally having true freedom.
This is a mountain range in North Korea. Over 600+ years ago Jin Mo-Ri was placed beneath this mountain in a seal.