Part 2 begins with a description of how ancient the Marabar hills and caves are. The caves, which are dark and all alike, are about twenty feet in diameter. A narrow tunnel leads into them.
Aziz arranges the expedition to the caves that he had mentioned earlier. He does not really want to do this, but he has heard a story that Mrs. Moore and Adela are offended with him because no invitation has reached them. Fielding and Professor Godbole are also to come on the trip, but when the day comes they miss the early morning train from Chandrapore that goes to the caves. Aziz is distraught, because he thinks the expedition has been ruined. But Mrs. Moore encourages him, and he determines to ensure that he handles with trip competently, just to refute those who say Indians are incapable of responsibility.
On the train journey, Adela enjoys making plans for her future with Ronny, but Mrs. Moore has become apathetic about life. At sunrise, the train approaches the Marabar Caves. Aziz has gone to great trouble to arrange for the ladies to be transported the remaining distance on an elephant. When they are close to the caves, they stop to eat. Aziz is pleased because so far, everything is going well and according to plan. He entertains Mrs. Moore, to whom he is devoted, and Adela, with stories about Mogul Emperors of the past.
After Adela has confessed her desire not to adopt the mentality of the other Anglo-Indians she has met, they go inside the first cave. Mrs. Moore dislikes it. It is too crowded with villagers and servants, and she nearly faints. She also dislikes the echo in the cave. As a result of this bad experience, she decides not to visit another cave, and she gives permission for Aziz and Adela to go alone to the next one. They are accompanied by only one person, a guide. Mrs. Moore remains behind in a deck chair, but she is tired, and this soon turns into despair. She feels that nothing has value. She loses interest in everything and doesn't want to communicate with anyone.
The visit to the caves is the key event in the novel. The first cave is significant for the effect it produces on Mrs. Moore. The echo is really a symbolic point about the Indian religious philosophy. A famous passage in the Upanishads, which are revered Indian scriptures, is "I am That, Thou art That, all This is That." This means that everything in creation, from the highest to the lowest, is an expression of Brahman. All the diverse forms of life are really only manifestations of the one life, the divine consciousness, that takes on different forms. So in the cave, whatever sound is made, the echo sends it back as a "boum" sound. It makes everything the same. This is too much for Mrs. Moore, who has been brought up on Protestant Christianity, with its concern for ethical conduct, for distinctions between right and wrong. As Forster wrote elsewhere, "The Hindu is concerned not with conduct, but with vision. To realize what God is seems more important than to do what God wants" (quoted in Wilfred Stone, "The Caves of A Passage to India," in A Passage to India: Essays in Interpretation, edited by John Beer, Barnes and Noble, 1986, pp. 18-19). This invasion of Mrs. Moore's mind by a philosophy that is so different from what she has been brought up to believe is her undoing.