Hello. You forgot to mention that this question is about the book "The princess Bride". It is important that you always provide all the information necessary for your question to be answered the way you deserve.
Answer:
The Cliffs of Insanity is a setting present in "The princess bride". This scenario is characterized as a cliff of 350 meters, difficult to climb and very unstable geologically, since it did not provide enough support for those who dared to climb. It is on this cliff that Princess Buttercup's abductors try to escape the "man in black" who is following them. Believing that this man will never be able to climb the cliff.
Evidence of the text is:
"The ascent started fifty meters above the water level, leaving two hundred and fifty meters. More than all of them, the Sicilian was afraid of heights. All of his nightmares, which always lurked in his sleep, involved falls. So, that terrifying climb was very difficult for him, clinging to the giant's neck. Or, at least, it should have been very difficult. He didn't allow it. From the beginning, when he realized as a child that his hunchbacked body would not conquer the world, he dedicated himself to the mind. He trained, fought and tamed her. Then, at that moment, a hundred meters high, in the darkness, when none of the trials prevented him from continuing to climb, he was not shaking. His attention was focused on the man in black. There was no chance that anyone had followed them so quickly."