In order to find this cache, you must complete the "Wispering Wonderful Waterfalls" Adventure Lab.
You will need a smart device with wifi and GPS capability to complete the Adventure Lab, which requires visiting the four locations of the Adventure Lab and answering a question at each one to earn a find. Completing the Adventure Lab will add four lab cache finds to your total. The stops can be completed in order. Although, if you are planning on finding the bonus cache I would complete Hemlock Falls last.
Download the Adventure Lab app to your smart device and look for "Wispering Wonderful Waterfalls" in the directory, or you can go directly there with this link. https://adventurelab.page.link/M65B
At two of the locations you will given the last 3 digits of the North and West coordinates for this bonus cache in your journal entry. Enter the last 3 digits into the Solution checker to get the cache location.