Imaginary voyage is a kind of narrative in which utopian or satirical representation (or some popular science content) is put into a fictional frame of travel account.
It is very archaic narrative technique preceding romance and novelistic forms. Two known examples from Greek literature are Euhemerus' Sacred History and Iambulus’ Islands of the Sun. Their utopian islands are apparently modeled from mythological Fortunate Isles.
Lucian's True History parodizes the whole genre of imaginary voyage, and in his foreword Lucian cites Iambulus as one of objects of parody. Photius states though in his Bibliotheca that its main object was Antonius Diogenes' The incredible wonders beyond Thule, a genre blending of fantastic voyage and Greek romance which popularized Pythagorean teachings.
The first to revive this form in the Modern era was Thomas More in his Utopia (1515), to be followed a century later by proliferation of utopian islands: Johannes Valentinus Andreae's Reipublicae Christianopolitanae descriptio (1619), Tommaso Campanella's The City of the Sun (1623), Francis Bacon's New Atlantis (1627), Jacob Bidermann's Utopia (1640), Denis Vairasse' The history of the Sevarambi (1675), Gabriel de Foigny's La Terre australe connue (1676), Gabriel Daniel's Voyage du monde de Descartes (1690), François Lefebvre's Relation du voyage de l’isle d’Eutopie (1711), as well as many others.