ADVENT was ported to the PDP-10, and expanded to the 350-point Classic puzzle-oriented version, by Don Woods of the Stanford Artificial Intelligence Laboratory (SAIL). The game is now better known as Adventure, but the TOPS-10 operating system permitted only six-letter filenames. All the versions since are based on the SAIL port.
David Long of the University of Chicago Graduate School of Business Computing Facility (which had two of the four DEC20s on campus in the late 1970s and early 1980s) was responsible for expanding the cave in a number of ways, and pushing the point count up to 500, then 501 points. Most of his work was in the data files, but he made some changes to the parser as well.
This game defined the terse, dryly humorous style now expected in text adventure games, and popularised several tag lines that have become fixtures of hacker-speak: "A huge green fierce snake bars the way!" "I see no X here" (for some noun X). "You are in a maze of twisty little passages, all alike." "You are in a little maze of twisty passages, all different." The "magic words" xyzzy and plugh also derive from this game.
Crowther, by the way, participated in the exploration of the Mammoth & Flint Ridge cave system; it actually *has* a "Colossal Cave" and a "Bedquilt" as in the game, and the "Y2" that also turns up is cavers' jargon for a map reference to a secondary entrance.
See also vadding.
[Was the original written in Fortran?]