When you build the dungeon you need to wait for it to empty its stocks, once it is is ready to be restocked a pink "play" icon appears on top of it.
The goal of this game is to reproduce the sequence of colors. Look at the lights being played in a random order, after which you must reproduce that order by pressing the lights.
You will have a surprise when you reach a sequence of 8 lights!
Here is an exemple video with the game "simon"