chunk: By his account, the speaker is kidnapped by fellow members of a secret society, because he is suspected to be a threat to their secrecy. (This was likely based on the 1826 kidnapping of William Morgan and the start of the Anti-Masonry movement.) I-Am-The-Man is taken to a cave in Kentucky; there he is led by a cavern dweller on a long subterranean journey. It becomes an inner journey of the spirit as much as a geographical trip through underground realms.
  The book blends passages on the nature of physical phenomena, such as gravity and volcanoes, with spiritualist speculation and adventure-story elements (like traversing a landscape of giant mushrooms). The whole ends with a summary letter from "I-Am-The-Man" and a conclusion from Drury. Subsequent editions of the book added various prefatory and supplementary materials.