The Epic Campaign
Not truly a plane, the Blind Eternities are the space between planes in the Multiverse which is filled with chaotic and powerful energies. Only spark-users, and the most powerful, godlike beings can enter it and survive its rough environment.
At the beginning of time, after the Creator birthed the First and before the rise of theThree Prime Evils and the Gods, he looked out on the void and created the Old Planes. To protect these planes from each other, he created the Blind Eternities, and a being to watch over it. Since then, the number of planes have expanded to almost countless number.
After the First birthed the Gods, he also created all of the humanoid races. To do this he drew directly from the Blind Eternities power and life, and severed it from the races. But, ultimately, he could not fully remove the Eternities from them, and vary rarely among people one is born with a spark, a direct connection to the Blind Eternities.