If you follow the western edge of the part of the isle that bumps up south, it will be in the forest, or if you head directly west from the dock and go a couple stride lengths south you should run in to it also.
All the way to the left at the end of the sandy part.
Head East from the town on Plains Isle. If head along the path between the houses though the town, the riddle box is almost due East.
7 strides due north of the dockhouse, then due west :)
It is in the forest in the center of the top of it.
Bottom Right of the Isle.
There is no riddle box on Square Isle.
in a bolder
the top
It is near the beach in east corner of the isle.
About halfway between the dock and the eastern end of the isle, by the northern beach
Go Directly West from the dock, and you will see it in a group of trees somewhere in the middle of the isle:)
there is no riddle box
There none.
In the northwest corner of the isle :)
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's near the north-eastern side of the forest
Switch Horses
On the light green bit between the three forests just south of the top river. You can find a screenshot of the location in related links.