The Ryukyu Islands is the 1,200 km chain of small islands located in southwestern Japan. During the Late Pleistocene, some of the islands remained more than 100km apart and invisible to each other beyond the horizon. This region also possessed one of the world’s strongest ocean currents, the Kuroshio. Despite these difficult circumstances, many of these islands had been occupied ~35,000–30,000 years ago by modern humans. Our experimental program called ‘Holistic Reenactment Project of Voyages 30,000 Years Ago (2016−2019)’, organized by the National Museum of Nature and Science, Tokyo, and the National Museum of Prehistory, Taiwan, was designed to identify the actual challenges faced by Palaeolithic voyagers in this region (https://www.kahaku.go.jp/research/activities/special/koukai/en/). By introducing findings from this at-sea experiment, we discuss key elements required for a deeper understanding of ancient sea crossings, as well as advantages and disadvantages for both simulation and on-site experimental studies.