Once upon a time there was a lonely bench and scraggly tree planted a pocket of soil amid a sea of concrete and rubble in what was called a "park". No one visited the park and the bench was very lonely, until one day a geocacher came across the spot and realized its potential.
That cache has since been archived, but in the meantime the park has received a dramatic makeover. Gone is much of the concrete and rubble; in its place are myriad new plantings, mulch and a gravel footpath, along with a revitalized shoreline. The park is now clearly defined from its surroundings, and includes a nicely themed bike rack and some colorful Mondrian-inspired bollards. There's still the issue that the park is far away from any houses or businesses, has almost no parking, and has essentially no signage to let you know of its existence, but at least it's now a pleasant spot to stop for lunch (or a cache) if you know about it.
You're looking for a small plastic container away from the main park area, which should help with the search if there are any muggles loitering on the bench.