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.
Zork
The first adventure game, "Colossal Cave Adventure", was written by Will Crowther in FORTRAN on the DEC PDP-10 at BBN in 1975. "Colossal Cave" is a basic treasure hunt that takes place in an analog of Mammoth Cave. The game uses a simple two-word parser that later adventure games imitated. PDP users quickly spread "Colossal Cave" around their community, including a Stanford University computer used by Don Woods in 1976. Woods contacted Crowther and received his permission to make an improved version which also spread to many locations, including the PDP-10 systems at MIT.