Agathys
All the portals at the centre of Porphatys' planetoids lead to the singular orb of Agathys. Agathys' deathly-cold surface is solidly encased in mile after mile of black ice streaked with red, vein-like cracks.
Geography
Agathys' black ice bears no underworld, though the sheets do sometimes crack into sharp crevasses, swallowing petitioners. These close with relative speed, trapping the unfortunates and then crushing them slowly. The air of Agathys rings with their screams.
Climate
The air of this black-ice planet is as thin as its starless sky. Breathing creatures need to keep still to avoid hypoxia, while creatures with a vascular system need to move constantly to avoid freezing solid.