This is a letterbox hybrid, which means there is a stamp located in the cache that is not a trade item.
You are looking for a medium sized peanut butter jar, located at the posted coordinates.
I make no guarantees that the writing instrument in the cache works, so suggest bringing your own. I also suggest bringing your own stamp pad if you wish you use the stamp.
I used to have a challenge about 25m from here - this cache is in a slightly different spot and should be a litte easier to get to.
Please replace as found and cover it well, so it can't be seen from the park.