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 famous archeologist (in the previous adventures he recovered a couple of great treasures) who squandered most of his wealth. Adding the nostalgia for his adventurous youth to his financial troubles, he chooses to embark on a last expedition to recover the gold of the Chibcha (a pre-columbian civilization).
The adventure begins when you reach the remnants of the main Chibcha city. Your goal is to find the hidden treasure.