This question might seem a little strange, but something has always nagged at the back of my mind about the Underworld - you've written that it's on an opposite schedule from the world above. Does the sun rise fully when it's daytime for Aidoneus and Perse

Do you know that light that comes after sunset when there are large clouds in the sky?  Not the pink kind from low clouds, but that brilliant half light that reflects off the clouds and down onto the land?  And there are no shadows, just diffuse low light coming from everywhere?  That’s about how I imagine the Underworld looks as it reflects up from the River Styx.

The sun never “rises”, but the diffuse light dawns and wanes like it would through fog. I picture that sort of light cast across wide expanses and dark surfaces, making the world no brighter than a cloudy day in the middle of winter.  Mist hangs above constantly, forming a “sky” of sorts, or at least something besides the encroaching blackness of Erebus when you look up. The low light desaturates everything, and the natural browns and reds look even darker.

The ground itself is all basalt rock, regolithic rubble, and obsidian flecks. Pebbles in dark shades of black, gray and brown, and sticking up through that unforgiving surface are stalks of asphodel, everywhere.  There is no wind, and no movement in the poplar trees to make their leaves shimmer between black and white.  So they’re dark from a distance and look lighter when you’re right under them.  Except for the poplar tree with the golden boughs right outside the palace.

The River itself is a muted blue, light enough to light up the mists above and blue enough so that it looks like the sky.  The blueness picks up the color of the cypresses, making them look even darker, it sharpens the color of the asphodel flowers, making them contrast even more with the red veins on each petal.

That’s how I imagine the Underworld.