No there isn't. I personally searched the isle and asked the help and none are on the island.
there is no riddle box
There none.
In the northwest corner of the isle :)
It's near the north-eastern side of the forest
There isn't a riddle box on every single Isle, but most have one... so there may not be one on Brown,but there might be...
It is by the southern south west edge of the light green grassy area in the center. -CalicoFilly
in a bolder
Close to the western corner
It is South and slightly East of the dock house on Prairie Isle.
It is on the top center of the forested part.
It is near the beach in east corner of the isle.
the top