The Twelve Heaven Mystery Realms opened every hundred years, but this period of a hundred years was only an estimate. Sometimes it would be ninety-plus years, while at others, it could be a hundred-plus years; there was no specific date.
These were the Mystery Realms that belonged to the north region. There were uncountable previous cases when cultivators obtained great rewards from within which helped them to accomplish great ventures. It was rumored that the current four most powerful great sects had gained humongous rewards in the Twelve Heaven Mystery Realms, which allowed them to stand out and claim great success out of a multitude of other sects and ascend to become the four most powerful sects.
Exactly what kind of rewards they had gained within, of course, the four great parties were not willing to divulge. This was, after all, their biggest secret.