Open world
There is no consensus on what the earliest open world game is, due to differing definitions of how large or open a world needs to be. Ars Technica traces the concept back to the free-roaming exploration of 1976 text adventure game "Colossal Cave Adventure", which inspired the free-roaming exploration of "Adventure" (1980), but notes that it wasn't until 1984 that what "we now know as open-world gaming" took on a "definite shape" with 1984 space simulator "Elite", considered a pioneer of the open world; Gamasutra argues that its open-ended sandbox style is rooted in flight simulators, such as SubLOGIC's "Flight Simulator" (1979/1980), noting most flight sims "offer a 'free flight' mode that allows players to simply pilot the aircraft and explore the virtual world". Others trace the concept back to 1981 CRPG "", which had a free-roaming overworld map inspired by tabletop RPG "Dungeons & Dragons". The overworld maps of the first five "Ultima" games, released up to 1988, lacked a single, unified scale, with towns and other places represented as icons; this style was adopted by the first three "Dragon Quest" games, released from 1986 to 1988 in Japan.
Adventure game
Due to a lack of content restrictions, some of Japan's earliest adventure games were also bishoujo games with "eroge" content. In 1982, Koei released "Night Life", the first commercial erotic computer game. It was a graphic adventure, with sexually explicit images. That same year, they released another "eroge" title, "Danchi Tsuma no Yuwaku" ("Seduction of the Condominium Wife"), which was an early adventure game with color graphics, owing to the eight-color palette of the NEC PC-8001 computer, and role-playing video game elements. It became a hit, helping Koei become a major software company. Other now-famous companies such as Enix, Square and Nihon Falcom also produced similar "eroge" in the early 1980s before they became famous for their mainstream role-playing games. In some of their early "eroge", the adult content is meaningfully integrated into a thoughtful and mature storyline, though others often used it as a flimsy excuse for pornography.