The True History (Greek: Ἀληθῆ διηγήματα, Alēthē diēgēmata; Latin: Vera Historia) by Lucian (c.115-c80 CE) is a parody of traveller's tales which features journeys to the moon, and to the Isles of the Blest. It influenced a later genre of fantasic voyages to which works by authors such as Rabelais and Swift could be ascribed, and has been called the first work of science fiction.
Free online texts
The Classics pages: Lucian - Greek science fiction. HTML format.
Gutenberg: Lucian's True History, translated by Francis Hickes. Multiple formats.
Loebulus: L014 - Lucian -- Lucian I: Phalaris. Hippias or The Bath. Dionysus. Heracles. Amber or The Swans. The Fly. Nigrinus. Demonax. The Hall. My Native Land. Octogenarians. A True Story. Slander. The Consonants at Law. The Carousal (Symposium) or The Lapiths. Public domain Loeb edition, Greek-English parallel text. PDF format.
The Lucian of Samosata Project: The True History, translated H.W. Fowler and F.G. Fowler. HTML format.
Perseus: Greek text. HTML and XML formats.
Sacred Texts: A True Story, translated by A.M. Harmon (1913). Parallel Greek/English HTML text.
University of Adelaide (Internet Archive): The True History, translated by H.W. Fowler and F.G. Fowler. Multiple formats.