Etidorhpa, or, the end of the earth: the strange history of a mysterious being and the account of a remarkable journey is the title of a scientific allegory or science fiction novel by John Uri Lloyd, a pharmacognocist and pharmaceutical manufacturer of Cincinnati, Ohio.

Ideas presented in Etidorhpa include practical alchemy, secret Masonic orders, the Hollow Earth theory, and the concept of transcending the physical realm.

[5] Substances from marijuana and opium to nightshade, henbane, jimsonweed, and psilocybin mushrooms have been suggested as possibilities,[6] although no real evidence on the matter is available.

The mysterious stranger, also known as The-Man-Who-Did-It, relates events that supposedly occurred thirty years earlier, during the early part of the 19th century.

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).