Technically speaking, the River Styx isn't an underworld realm – it is a liminal space that touches on all known underworld realms. Manifesting as a great flowing river whose far shore is dimly visible through the mist, the River Styx is cast eternally in twilight. Its near shore is thick clay-like mud a deep black color, with patches of stones and the occasional bone interrupting its smoothness. The shore descends down to the water's edge where a panoply of tall grasses occasionally ripple and whisper in a wind that living flesh never feels.
The calm surface of the black waters are occasionally broken by the shade of one of the dead, surfacing to try and clutch at a life it has already lost. These spirits are often borne away by a tide that affects only them.
Because the Styx touches on all places in the earthly realm, it is possible for those canny in its metaphysical geography to enter the realm, travel a carefully calculated distance, and then re-emerge in the earthly realm a significant distance away from where they began. There is a danger navigating the shoreline in this way, however: those who wander these realms over-long may find the call of the river pulling at their body and spirit in dangerous ways.
- Navigation Check: A character must make an Expertise (Underworld) check to avoid becoming lost, at a DC equal to the Distance Rank being traveled. This takes an amount of time to traverse equal to the (Distance Rank minus 10) as a Time Rank. So, traveling 120 miles (Distance Rank 15) is a DC 15 check, and takes 4 minutes (Time Rank 5) to traverse.
- Resisting the Call: The effects of resisting prolonged exposure to the call of the Styx are handled as a set of Progressive Afflictions (Necromantic). The eroding effects of the Styx on mortal bodies is handled as a Fortitude save, and the melancholy siren's song that calls even the living into its black waters is handled as a Will save.
- Fortitude: Fatigued > Exhausted > Incapacitated. Waves of exhaustion and the desire to simply lie down and cease moving overcome the living while in the realm of the Styx.
- Will: Entranced > Compelled. The river calls to the mind. Those who are entranced merely stand on the shore, gazing out at the waters, while those who are compelled actively seek to immerse themselves in the waters.