This one isn't meant to be tricky or hard to find. It's just a simple little cache in a nice location: a quiet spot along the edge of the Lynnfield Marsh (aka Reedy Meadow), the largest freshwater cattail marsh in Massachusetts.
Your search will take you to the former location of Pleasure Island, an amusement park in Wakefield that once covered 80 acres and was billed as "Disneyland East". Pleasure Island opened in 1959 and survived only until 1969, but during its short existence it was a major tourist attraction on the North Shore of Boston, drawing hundreds of thousands of New Englanders and tourists from all over the country. The Friends of Pleasure Island web site has photos and information about the various attractions that were part of the amusement park. (Thanks to GeoRatz for pointing out this web page.)
To this day, there are only a few physical reminders of the amusement park: the exit signs along Route 128 that read "Pleasure Island Road, Exit 42" and the short stretch of Pleasure Island Road that now quickly becomes Audubon Road.
The cache is a short walk from a few different parking options. If you park across the street, be careful of traffic as you cross the road. Better yet, use one of the two available crosswalks, either just north of the cache location or at the southern end of Audubon Road.