The Zork games are seminal influences on many games to follow, and are the examplars par excellence of the heydey of the text adventure. Purely text in nature, they cast doubt on the very term "video game" -- nothing "video" about them. A description is presented to you; you type in your response (and hope that the parser understands you), grab items, and combine them to solve puzzles. Though derivative of earlier academic games like Crowther's Colossal Cave, they added an element of humor and a puzzle complexity that modern games rarely aspire to.
When the game has finished loading, click on the text to begin typing. If the black window appears blank, reload (or just type 'look').
Every gamer should play these games--once at least. For historical reasons--but also to understand what has been lost by the focus on improved graphics at the expense of excellent writing.
Today, the Zork games are owned by Activision, which has released them for free download.
Play by clicking on the black box above and typing; if no black box appears, you need to install Java on your machine.
But! playing here doesn't allow you to save your progress. If you want to do that, you need to download and install a Z-machine interpreter on your computer, then download this game's file and open it with that interpreter.
(If the black box, but no text, appears, try reloading and waiting a bit.)