This letterbox hybrid is called "Good Thinking!" and I hope you think wisely in your quest to find it.
Park at the listed coordinates. This is a good street parking location (be sure and obey the parking on one side of the street only signs).
You should be standing in front of a marker post. This is known as Lot 90. In 1832, Christian Federick Denke and his wife Maria Steiner Denke, built this as their retirement home. Federick had served as the minister of Hope and Friedburg Moravian churces. This was the second house built on Factory Row.
From this sign post, walk south along the side walk, passing the Ackerman house, for a distance of approximately 115 double paces (a double pace is counted each time the same foot hits the ground).
You should now be standing in front of another sign post with information about the "Brewery." The brewery is no longer here. Because of financial problems and the inability to secure a brewmaster, the facility closed in 1805.
From the "Brewery" sign post, walk on the sidewalk in a direction of 90º along a split rail fence for approximately 27 double paces. You have now reached the paved walking trail.
Begin walking south along this trail for approximately 127 double paces crossing over a wooden bridge. Stop in the center of the walkway.
Face west, and walk about 10 double paces. The letterbox you are seeking is located at the base of a hollow tree near the creek.