I remember a game a friend of mine copied on my HD, Microsoft DOS days. Me and another friend did not know anything about the game: there was just this black screen (or was it green? - I can't remember) and a white command prompt.
As a joke we typed 'hi' or 'who are you', something like that, and laughed when we suddenly got an answer, one that made sense.
We soon learned that by typing the right commands you'd move through a sort of dark corridor, an underground network. In this maze there were several puzzles you had to solve if you wanted to move forward.
We had no help-function, we had to think of the right way, the right questions and the right actions ourselves. We got stuck several times, days, weeks, would pass before finding the solution.
I had the entire maze drawn out on a piece of paper; without it we were lost: you had to move forward and back quite often.
We never made it to the end, we simply never found the right solution to a road block.
But my, we had such a great time! And the only thing needed: your own imagination and a white blinking prompt…
No idea what the name of that game was.