Tokyo parks are made for slowing down. Somebody put a lot of thought into designing everything just so — the pond, the landscaping, this tree here, that tree there. Find a bench and take it all in.
Arisugawa-no-miya Memorial Park is an excellent example of Tokyo tranquility.
My favorite place to stop before some quality park bench time is Boulangerie Burdigala about a block away for a delicately flaky pear pastry.