The entire game takes place in the year 948 GUE although the passage of time is not notable in gameplay. The player steps into the deliberately vague role of an "adventurer". The game begins with no preface near a white house in a small, self-contained area. Although the player is given little instruction, the house provides an obvious point of interest.
When the player enters the house, it yields a number of intriguing objects: an ancient brass lantern, an empty trophy case, and an intricately engraved sword. Beneath a rug, a trap door set into the floor leads down to a dark dungeon. Soon the player is encountering dangerous creatures, including an axe-wielding troll, a cyclops and a nimble-fingered thief. What initially appeared to be a dungeon is actually a vast subterranean land: the Great Underground Empire.
The ultimate goal of Zork I is to collect the Twenty Treasures of Zork and return them to the trophy case in the white house. The Twenty Treasures are:
Finding the treasures requires solving a variety of puzzles, including navigating a brutal maze of identical rooms, an exorcism, and the successful manipulation of Flood Control Dam #3 without going over Aragain Falls. Once the first nineteen treasures are added to the case, the Ancient map appears in the case with the other treasures, giving the adventurer instructions for finding the Barrow, the path to Zork II.
Infocom did not begin their tradition of including feelies, or extra items related to a game, until the 1982 release Deadline. Later re-releases of the game, however, were packaged with:
The booklet The Great Underground Empire: A History, by "Froboz Mumbar"
A map roughly corresponding to a portion of the game's area
The opening text of Zork I is among the most famous descriptions in computer games:
West of House
You are standing in an open field west of a white house, with a boarded front door.
There is a small mailbox here.
This is quite simplistic when compared to Infocom's later games, many of which started with screenfuls of introductory text.
Several of the game's situations and descriptions have become iconic within the field of interactive fiction, such as the brass lantern and the "Elvish sword of great antiquity".
Zork I also introduced the famous grue, a "sinister, lurking presence" who kills adventurers who go exploring in the dark. Grues appeared (or, at least, were mentioned) in many subsequent Infocom adventures, right up to the 1997 graphic adventure Zork Grand Inquisitor, published by Activision.
The original version of Zork I was published by Personal Software and simply called Zork. It was distributed in clear plastic bags containing only the game disk and a 36-page booklet. Infocom's first "self-published" version of Zork I was in the so-called "Folio" format which included a single piece of paper describing how to run the game. The feelies noted above were only introduced when Zork I was re-released in the "Grey box" format.
Although the back of the Zork I "Grey box" depicted a zorkmid coin included with the other feelies, production difficulties led to the coins' omission from the packages. Zorkmid coins were not included as feelies until the release of the Zork Trilogy boxed set.
The name of Aragain Falls was created by spelling the word Niagara backwards.
