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
The most famous early Japanese computer adventure game was the murder mystery game "Portopia Serial Murder Case", developed by Yūji Horii (of "Dragon Quest" fame) and published by Enix. Its development began in 1981, and was released in 1983. The game was viewed in a first-person perspective, followed a first-person narrative, and featured color graphics. Originally released for the PC-6001, the player interacts with the game using a verb-noun parser which requires typing precise commands with the keyboard; finding the exact words to type is considered part of the riddles that must be solved. The game was non-linear, which includes exploring an open world, a branching dialogue conversation system where the story develops through entering commands and receiving responses from other characters, and making choices that determine the dialogues and order of events as well as alternative endings. It also features a phone that could be used to dial any number to contact several non-player characters. The game was well received in Japan for its well-told storyline and surprising twist ending, and for allowing multiple ways to achieve objectives. Hideo Kojima praised the game for its mystery, drama, humor, 3D dungeons, for providing a proper background and explanation behind the murderer's motives, and expanding the potential of video games. The game has also been compared to the later-released "Shadowgate" where the player must examine and collect objects, and find their true purpose later on. According to Square Enix, "Portopia" was "the first real detective adventure" game.