The placer of the Mystery Falls LB lost the clues and asked that
anyone who had the clues please post them to this website. So here
they are:

Mystery Falls Letterbox
Placed 5/30/02 by Stephani, John, John Turner and Maggie the Dog
Duration of this walk could be anywhere from about an hour to three
hours, depending.

This letterbox is hidden along a section of the Narragansett Trail
near Green Falls Pond. There are several ways to access this trail
but we recommend parking at the green gate on Green Falls Road. To
get to Green Falls Road: turn on to Sand Hill Road from Route 49 in
Voluntown (this turn is marked by the Studio Farm which sits on the
corner); after turning left than right around one of the Palmer farms
in the area Green Falls Road goes straight while Wheeler Road bears
to the right; Green Falls Road quickly turns to a dirt road; the
Narragansett Trail (blue blazed) crosses once and a bit further up on
the left you will see the green gate; park here.