Non Hoi Park is Toyohashi's big all-in-one family day out: zoo, botanical garden, amusement area, and natural-history museum on a wide site south-east of the centre. It is not subtle, but it is useful and genuinely popular with local families.
The natural-history museum is the best reason for adults to go, especially if weather turns bad. With children, the park can easily take half a day. Without them, treat it as a relaxed add-on after Futagawa rather than the main reason to stop in Toyohashi.