You'll need to finish my Tour the Chain of Lakes (By Land!) Adventure Lab first in order to get the information needed to find this bonus cache.
If you're coming here after completing that Adventure Lab, I hope that you enjoyed it! Here's a reward that brings you to the spot along the Chain of Lakes where I've spent the most time (100+ visits over the years).
As you complete each location of the Adventure Lab, the journal entries will give you 6 keyword letters (and 6 numbers). Unscramble the letters to get the six-letter keyword, then swap out the letters for the numbers and enter them, in order, to get the Final coordinates: N 44° 57.xxx' W 93° 19.xxx'
Stealth is very important at this location, so during the summer I would recommend searching in the early morning. During the other seasons, you shouldn't have to worry about muggles as much. (If you *must* search when there are lots of people around, please read the hint so that you can quickly sign the log without drawing too much attention to yourself.)