Love how glaringly obvious this one is, yet it's also something so easily overlooked. This is fun! :D
A third one has been found. In a recent Blue post the image has been edited showing a map to thousand needles. There is an underwater cave at 44.0, 37.3 with the dirt mound inside.
i found the thousand needles satchel inside the cave at: 43/31 (mapcoords) or -205/-682 cogs-bolts
Would like to clarify that this is actually under the water. I flew around trying to find it thinking the coords pointed to the 'large body of water' in general, as this guide states it is 'by the' water.
Why am I doing these, they're useless. 240 gold, wow.