Odaiba (お台場) is a large artificial island in Tokyo Bay, Japan, across the Rainbow Bridge from central Tokyo. This is generally known as a date spot. You can either take a driverless train which goes over rainbow bridge, or you can take a boat from Asakusa. Both are pretty nifty. Personally, I’d take one there and the other one back.
The Shinjuku Gyoen National Garden (新宿御苑) in Tokyo, Japan is massive with a circumference of 3.5 km. We spent hours walking around and viewing the garden’s three distinct styles: French Formal, English Landscape, and Japanese traditional. What a place to run in the grass and get lost!