What does the entrance to underworld look like Percy Jackson and lightning thief?

In Rick Riordan's *Percy Jackson & the Lightning Thief*, the entrance to the Underworld is described as a giant, swirling vortex of mist at the bottom of the River Styx. This mist is said to be cold and wet, with a *weird, ghostly glow* that makes everything seem hazy and indistinct.

Here are some key details from the book that describe the entrance:

* "The mist swirled around us, thick as fog, and the air turned ice-cold."

* "I could see through the swirling mists, down into the dark water. The current was so strong, it would rip a boat in two."

* "The Styx was a black river, a swirling vortex of mist. We could hear the roaring of the current and the whispers of those who had drowned in its depths."

The entrance is also described as "a place where the living shouldn't be," emphasizing the dangers of this gateway to the Underworld.

While it's not explicitly stated what the Underworld itself looks like, the entrance's description paints a picture of a cold, dark, and ominous place, preparing the reader for the sinister and dangerous realm that lies beyond.