Zork was one of the first computer 'adventure games'. It was text based, with simple geometric graphics of landscape (if my memory serves me right, though that might have been another game called 'Adventure'). It was played on the old green screen CRT. A combination of mapping issues, tricks, puzzles, riddles and such like problems, it was great fun and highly addictive.
It looks like it has generated a minor academic history (as I guess does the early days of personal computing generally). Here, for example, is a recent accademic paper on it. It's a guide to caves upon which the game's map was based. I haven't read it all, but the pictures are amazing!
Thanks to Yehuda for the link.
2 hours ago