“Piper,” Annabeth said sadly. “It’s the Mist.”

“Missed … what?”

“M-i-s-t. It’s a kind of veil separating the mortal world from the magic world. Mortal minds—they can’t process strange stuff like gods and monsters, so the Mist bends reality. It makes mortals see things in a way they can understand —like their eyes might just skip over this valley completely, or they might look at that dragon and see a pile of cables.”

The Lost Hero, Chapter IV