We finally found the solution, but we don't really understand how we were supposed to find it with the clues in play. At first we thought we'd have to search the internet for clues like the bison, the mountain, or the elements in the letter, but in the end we didn't really understand the relationship between the clues provided and the solution to the riddle.
However, the concept of searching for information on the Internet according to the clues in play can be interesting, and the game is very pretty and has a nice atmosphere!