Mill Ends Park, Google Maps:

Teensy, quirky plantings area on a median strip, billed as the world’s smallest park.

Mill Ends Park, Wikipedia:

Mill Ends Park (sometimes mistakenly called Mill’s End Park)[1] is the smallest urban park in the United States. It consists of 1 tree, located in the median strip of SW Naito Parkway next to Tom McCall Waterfront Park along the Willamette River near SW Taylor Street in the downtown core of Portland, Oregon, United States.