The Chrono Crater is a volcanic-type pool that erupts occasionally, and is rumored to give special powers, or even make one immortal. It's first appearance took place in the 2013 LEGO Ninjago: Masters of Spinjitzu graphic novel Stone Cold.
The Crater is connected to the Time Ninja because it is the cause of his elemental powers. He attempted to become immortal by standing near the crater when it was about to erupt, but was instead given the power of Time.
The crater has not been shown in any other works of media, aside from the book it first appeared in.