Unsent letter

Unsent letter may refer to one of the paper notes $$

Location
Three different unsent letters can be found at different locations:
 * One can be found on a barrel at Hunter's Ridge, at the foot of a guard tower on a platform at the south end of the area.
 * One inside of the upper rooms in the Palace of the Winding Path.
 * One can be found by inspecting the painting in David Thorpe room during Strange Bedfellows.