It's a textual adventure (some graphic embellish it, but is purely decorative and has no role in the game).
You give commands usually composed by a verb plus a noun (e.g. "go north", "examine desk", "drink potion") and are told what happens ("you cannot go in that direction", "there is a pen on the desk", "you feel reinvigorated"). You have to explore the locations, collect items, use them when appropriate and in general imagine how to overcome the various problems in order to accomplish the final goal of the adventure.
You are Terry Jones, a young archeologist determined to find the tresure of the Aztecs. The adventure begins when you are travelling towards Machu Picchu and your guide (and the mule with your equipment) die falling into a ravine. Your goals are to survive and to find the treasure.