Colossal Cave Adventure (shortened to Adventure on my Atari ST) was the first interactive fiction computer game I played. According to Wikipedia, it was also the first adventure game to be written.
The premise was simple enough - you had to enter a colossal cave (based on the real life Mammoth Cave in Kentucky) and bring all of the treasure you find back to a small building outside. You controlled your character by moving the around with the compass points and other commands such as 'kill', 'feed', 'drop', 'get' and 'look' amongst others.
I always enjoyed wandering around the Colossal cave and enjoying the strange and funny encounters. It had everything - a pirate, a troll, a dragon, dwarves, a bear and much more. I never won this game. My highest score was something rubbish like 76/350. The decisions were a little arbitrary and required trial and error and I never had the patience to try everything. There were some good tricks that you needed to learn such as learning how to kill the dragon, transporting the vase back to your house safely and getting that elusive final point. I didn't find most of these things out until I read a walkththrough but the things I did find out I felt very smug about.
Colossal Cave has been an inspiration to other interactive fiction in various ways, not least the use of the phrase 'Xyzzy'. There are even Xyzzy awards for interactive fiction.
The good thing about Colossal Cave now is that you can get it and play it for free in various ways and if you get stuck, you could find a walkthrough. If you have an Android phone, you can get a Colossal Cave app for free.
You can play the Colossal Cave Adventure here
You can download Colossal Cave Adventure here.
You can buy a book about interactive fiction here. The title, Twisty Little Passages, is another nod to a phrase from Colossal cave.