The game takes place in the Zork calendar 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 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, an intricately engraved sword, etc. Beneath the rug a trap door leads down into a dark dungeon. But what initially appears to be a dungeon is actually one of several entrances to a vast subterranean land--the Great Underground Empire. The player soon encounters dangerous creatures, including deadly grues, an axe-wielding troll, a giant cyclops and a nimble-fingered thief.
The ultimate goal of Zork I is to collect the Nineteen Treasures of Zork and install them in the trophy case. Finding the treasures requires solving a variety of puzzles such as the navigation of two brutal mazes and some intricate manipulations at Flood Control Dam #3.
Placing all of the treasures into the trophy case scores the player 350 points and grants the rank of "Master Adventurer." An ancient map with further instructions then magically appears in the trophy case. These instructions provide access to a stone barrow. The entrance to the barrow is the end of Zork I and the beginning of Zork II.
Open the mailbox. Get the leaflet and read it, then drop it. Go north twice and climb the tree. Get the egg from the nest and go back down. Go south and east. Open the window and enter the house by going west. The sack on the table contains a lunch; you can hold on to it as the alternate solution to a later problem (see "The Cellar Area and Maze", below), or eat it (but save the garlic) and drink the water in the bottle, if you like. The brown sack can also be used as a container. Go west. Get the sword and lantern. Move the rug and open the trap door. Turn on the lamp. Go down into the Great Underground Empire.
At any point underground, the Thief may come by and steal valuables from you. If this happens, don't worry; you'll get the treasure back at the end of the game. The Thief is hard to defeat in a fight. If he is already in a room when you enter, it is usually a good idea to leave immediately; giving him a treasure will also distract him from attacking you for one turn. The nasty knife from the Attic is a slightly better weapon against the Thief than the sword is. You also become a better match as you gain points, so save purposely attacking him for the very end of the game.
Go north. Kill the troll with the sword. Go west and enter the Maze. Go west, west, and up. Get the bag of coins. (The skeleton key opens a ceiling grating elsewhere in the Maze; however, doing so scores no points, and isn't necessary for anything else.) Go southwest, east, south, and southeast. Either say "Odysseus" to the Cyclops to scare him away, or give him the lunch and water from the Kitchen. Drop the egg if you haven't already given it to the Thief or had it taken from you. Go east twice and you're back in the Living Room. Now that you have found another exit from the GUE, the trap door will not close behind you. Open the trophy case and put the coins in it. Open the trap door and go down. Go south, then east. Get the painting, then go put it in the trophy case (west, north, up).
Go down the trap door. Go north, then east three times to the Loud Room. Type echo. Get the platinum bar. Scurry back (west, west, west, south) and put it in the trophy case. Return to the Loud Room (down, north, east x3) and go up, then east, then north. Get the matchbook and read it. Go north or east. Get the wrench and screwdriver. Push the yellow button. Go south twice back to the dam and turn the bolt with the wrench. Drop the wrench. Go west and wait until the reservoir empties. Go north. Drop the bottle if you still have it, and get the trunk of jewels. Take it back to the trophy case (south, southwest, southwest, west, south, up). Return to the Reservoir (down, north, east, north, northeast, and north). Go north again and get the air pump. Go north again and get the crystal trident. Go up, north, north, west, and then down to the Cellar. (Convenient, eh?) Go up and put the trident in the case.
Go east to the Kitchen, then up to the Attic and get the rope. Go back down into the Cellar. Go north, east, east, southeast, and east. Tie the rope to the railing and go down. Get the torch and turn off your lamp. Go south and drop everything but the torch. Go east and get the coffin. Open it and take the sceptre. Go west, then south. Ignore the candles and book for now and pray. You will be teleported to the forest. Go east, south, east, and enter the house. Put the coffin and sceptre in the trophy case. Return to the Temple (down, north, east, east, southeast, east, down, south), where you dropped everything, and get the matchbook and bell. Open the matchbook. Go south and get the candles and black book. Put out the candles. Go down, then down again. Make sure you're carrying nothing but the book, candles, bell, matchbook, and torch. Ring the bell. You will drop it, and the candles. Get the candles, light a match, light the candles, then read the book. Go south and get the skull. Drop the book, matches and candles. Go north, up, north three times, west, west, south, and up. Put the skull in the trophy case. Get the sceptre again while you are here. Return to the Temple (down, north, east, east, southeast, east, down, south) and collect all your belongings. (You should have the sack with air pump, lamp, sword, sack with garlic, screwdriver, sceptre, and torch.)
From the Temple, go south, down, north, north, north, east, up, east, east. At Dam Base, inflate the pile of plastic with the air pump. Drop the pump. Read the label, then drop it. Put the sword, screwdriver and sceptre in the boat before you get in; they are sharp and will puncture it if you board while carrying them. Get in the boat and launch. Wait for the river to carry you downstream. When you see the buoy, get it and go east to land. Get out of the boat. Open the buoy, take the emerald, and drop the buoy. Get the shovel. Go northeast and dig in the sand until you find the scarab. Drop the shovel and take the scarab. Go southwest, pick up all your items except the buoy and boat, and then go south twice. Wave the sceptre. Go west twice across the rainbow. You're carrying too much to get the pot of gold at the moment, so go southwest, up, up, northwest, west, and enter the house and put your treasures in the trophy case. Then come back for the pot of gold by going east, east, down, down, north from Behind House, and put it in the case too. (If the pot of gold is gone, then the Thief has stolen it. We'll get
it back at the end of the game.)
If you are carrying the garlic in the sack, take it out and carry it normally. From the Living Room, go down, north, east twice to the Round Room and go south twice. Touch the mirror and you will be transported to the north Mirror Room. Go north, west, north, west, and north. Get the jade figurine. Go east. Put the torch and screwdriver in the basket. Turn on your lamp. Go north, then down. Get the bracelet. Go east, northeast, southeast, southwest, and down twice. Go south and get the coal. Go north, back up the ladder and stairs and then go north, east, south, and north through the mine, then up and south to the Shaft Room. Put the coal in the basket as well, then lower it. Retrace your steps to the bottom of the ladder (north, down, east, northeast, southeast, southwest, down, down), go west, drop everything, and then west again. Get the items from the basket and go south. Open the machine, put the coal inside, and close it again. Turn the switch with the screwdriver. Open the machine and get the diamond. Drop the screwdriver. Go north and put the torch and diamond in the basket. Go east, pick up your items, and go back through the coal mine to the Shaft Room (east, up, up, north, east, south, north, up, south). Raise the basket. Drop the sword and take the diamond and torch. Go west, south, east, and south, then down to the Cellar and go put your treasures in the trophy case, including the torch.
Drop the garlic (or eat it, if you are silly that way). Go up to the Attic, pick up the nasty-looking knife, and drop the sword. Go west twice from the living room to the Cyclops room, then go up. Attack the Thief with the nasty knife. (If by chance he is not there, leave and return until he appears.) When you have killed him, take the chalice, the egg and the canary (and any treasures the Thief stole from you). Go down to the Cyclops Room and then east twice to the Living Room. Put the chalice and egg (and any other treasures you may have recovered) in the case. Leave the house, and go north twice into the forest. Wind the canary. Get the brass bauble. Return south and east to the house and put the canary and bauble in the case. Look at the trophy case, and you will find a map has appeared. Take it and look at it. Leave the house, then go south and west to West of House. Go southwest down the "secret path" which has appeared,
and enter the Barrow to the west. Congratulations, you're now in Zork II.