Slightly off the delightful Mercer Lake path, with minimal bushwhacking required.
You do need to be a bit of a "Metal Detector" to find this one. You're looking for a small black box, with only room for a log book and maybe a few small items inside. As the song says,
I've got something
To make you understand
Something hidden there
Underneath the land
They Might Be Giants, Metal Detector
Lbh jvyy arrq gb purpx haqrearngu gur ynaq.