"In the Walls of Eryx" is a science fiction story by H. P. Lovecraft and Kenneth Sterling, first appearing in the October 1939 edition of Weird Tales Magazine.

Set on the sweltering, jungle-covered surface of Venus, In the Walls of Eryx follows a seasoned Earth explorer working for a commercial crystal-harvesting operation. While searching for energy-rich crystals, he becomes trapped inside an invisible, maze-like structure of unknown origin—constructed by the native lizard-like Venusians. As he struggles to escape the alien trap, his supplies dwindle and his thoughts turn increasingly inward, confronting not only his own mortality but the ethics of humanity's exploitative presence on the planet.