|Location||Bal-Kriav, various systems|
This river was created in the Dawn Era by Bruh Kreniik. He had the foresight to make it a military highway between Ellubôz and Piranoth's Steps. While the worlds of this system were being built, Bruh Kreniik's agents learned that Piranoth was getting carried away with his powers of Creation and building too many worlds, too fast. Bruh Kreniik knew this did not bode well, since he believed that creating worlds required planning, order and discipline. He was correct in his thinking because in the Abyssal Release the name Piranoth's Steps would fall out of favor with its denizens (the demons) now calling it the Abyss. On the 110th world of the Abyss, the river Styx passes through a permanent rift linking it with the world Avernus. On both sides of this rift are deep fortifications with many dating to the Dawn War. They have been added to for thousands of years creating seemingly impregnable fortifications many miles deep. On the Abyss side, one hundred thousand demons man their walls and on the Avernus side there is an equally imposing army of devils. For the decision-makers on both sides, the defenses are so strong that neither have used the Styx as a route of inter-system assault since the Horgon Era. Failed naval expeditions litter the shores of the Styx for a hundred miles into Avernus. Thousands of hulks litter the shores and are often the abodes of some fiend or hellish critter of Avernus. After many wars and the deaths of millions on both sides, some find their way into or past enemy's defenses. These are often spies or assassins with the skill to evade hundreds of lookouts along a corridor of walled river some five miles long on the Abyss side, or eight miles long on the devil's.
The river Styx spans many worlds, with an unknown number of tributaries. It has branches flowing through some of the worlds of Pandemonium, the Abyss , Tartarus, Hades, Gehenna, and Acheron. The river is said to end at an ocean on Stygia, though some speculate that the beginning and end of the Styx are the same.
One of the Styx's tributaries periodically enters the world Bal-Kriav at a place called the Styx Fountain. The waters of the Styx, known for causing permanent forgetfulness, are reduced in power as they mix with the Underdark waters of Maitimírë. The granite cavern walls that touch the lake waters and all the way down the river leading to the Green Nebulous are tainted from contact with the Styx. The granite of the area that becomes tainted takes on the properties of Styx Granite.
As far as the Hells are concerned, the easiest road to the hells is via the Styx, for if it can be found on mortal worlds and the fee paid (to Charon or his charonadaemons), an admittedly perilous route to the hells is opened. The Styx passes eventually into Avernus, and thence to Stygia, before passing on to other places.