Mictlan's Cave is cold, damp and completely dark. The Cave ultimately removes any form of light that dare to penetrate the ever-changing shadows. Inky, deafeningly silent, and quite unfathomable, explorers (who are still alive) are unable to define how large this is.
It is also almost impossible to sense anything in the Cave and drives those who have weak wills into a state of numbness and abandon them in eternal darkness before the soul of the dead continues the exploration and enter Mictlan. Any attempt to perceive or understand this environment will fail even those who attempt to use their powers of darkness to traverse. The effect it has on your body is so heavy that the cave itself will try to erase your existence completely. The darkness of the cave finally ends when you actually reach Mictlampa (by this time, you are already dying or lost all your senses to the eldritch cave), the realm of the dead. Mictlan's Cooper is easy to find but if you are not a demigod child of the underworld, you will only lose your life-force to it.