The Thousand Realms was a world separated by the Black Tidal Sea. Supposedly, it was impossible to cross the sea to reach this place as the sea was filled with extreme dangers that both worlds couldn't fend off. Unless it's a high ranking deity above, it's pretty impossible.
However, Jin Rou was very confident as he had done a few times in the past. His knowledge about the Black Tidal Sea surpassed everyone else.
The Thousand Realms was a much bigger world compared to Nine Heavens. Furthermore, the cultivation here was more advanced than the previous.
This world was brilliant because it had been protected by immortal sovereigns, the recognized highest realm one could attain in this world. If it's compared to dao monarchs, the monarchs were a tad weaker.