At just two feet in diameter, Mill Ends Park in the median strip of SW Naito Parkway is officially the world's smallest public park. The Guinness record has been certified multiple times since 1971. The park contains a miniature statue of a leprechaun, planted flowers that are changed seasonally, and occasionally tiny swimming pools, diving boards, or other miniature features installed by park volunteers.
The park's claim to fame is entirely in the contrast: it sits among the regular-scale traffic and buildings of downtown Portland and looks exactly like a city park except in miniature. It's a 30-second detour from the Tom McCall Waterfront Park, which runs along the Willamette River directly across the street. Worth a brief stop for the absurdity.