After many days of Percy Jackson and Annabeth Chase falling down the pit into Tartarus, Annabeth saw a river at the bottom of the pit.

Annabeth: “Percy! Control the water at the bottom! We might survive!”

Percy used his powers to control the water and cushion their fall. Unfortunately, the pair landed in Cocytus, the River of Lamentation. Due to the river’s magic properties, the pair began feeling immense sorrow and misery of bitter souls.