The Crate From El Dorado

Your favorite Uncle Phileas has always shared your love for puzzles and riddles. That was part of the special bond you two shared, but Uncle Phileas has gone missing! Now, several months later, the trail has gone cold and there is no sign of him other than some rumors that he was in the golden city of El Dorado. One day this box arrives on your doorstep with no note or instructions. Could this be a clue to what happened to your Uncle Phileas?