The cache is not at the posted coordinates in the Whetstone Brook but is placed with a view somewhere nearby.
The views of Brattleboro can be amazing! Here is a mystery cache placed as a bonus to the "Views of Brattleboro" Adventure Lab. Download the Adventure Lab app to your smartphone and you'll pick up a bonus cache along the way. https://labs.geocaching.com/goto/Brattleboro
I've provided some optional parking coordinates to help you find a parking place. The cache is placed on flat ground with a view and is winter-friendly depending on clearing of the space nearby. it's a magnetic container that is out of sight. It is wheelchair accessible when snow has been cleared from the space. There is a fee to park but this can be done as a park and grab or as a walk-up if you park elsewhere.
If you are not an Adventure Lab user I may have left another way to get the coordinates if you are resourceful.