About the Container
You're looking for a magnetic key holder. There is plenty of information in the listing about how to find it and we don't want it to get muggled, so please replace it completely out of sight.
About the Location
The hiding spot is on a dirt path that runs along the Milwaukee River Greenway. It's not too difficult if the conditions are warm and dry. It can be a lot tougher if the conditions are muddy or icy.
There is no direct path down from the road. The best place to park for this one is the public parking lot a bit south of the location on Estabrook Parkway. From there go straight west across the park and make your way down toward the river. There is a lower path right next to the water and a path that's part way up the hill. This cache is on the upper path.
About the Spy Gear
It's a staple of spy movies and action movies for characters to have spring-loaded guns that pop out of their sleeves. One example is James West in the 1960s TV series The Wild Wild West who carried a Remington derringer that way.
Permission
Permission to place this cache was granted by the Milwaukee County Parks Department. Permit 481.