How does the author describe his exploration of the Mendip Hills in the nonfiction book, Underland?

MacFarlane goes caving in the hills with a guide named Sean. "This is clearly a strong place -- and it has drawn humans to it for thousands of years," MacFarlane writes of one site in the hills (45). Inside the caves in the hills, MacFarlane feels claustrophobic. "Crouched in that bare space, my heart hammers warning in my ears," (47). "I reach out and place a hand on the black rock of the first boulder, and the cold volts into me like a current, surging up my arm, petrifying me." In the end, MacFarlane depicts the Mendips as a beautiful landscape with a long history of human interaction, but still one that defies human comprehension, especially in its underground spaces.