A very popular park in the south of the city (noted for its Plum blossoms that flower in March, its excellent tennis courts, and convenience to the Domi shopping center...).
Minami Koen ("South Park") is like every child's dream come true.
In the lake you see ducks, turtles and jumping fish, lovely pagodas to sit in and relax, a swimming pool that costs almost nothing to enjoy during the summer, a baseball ground, and a small amusement park.
The amusement park has simple rides - rocket ships, the typical Victoriana merry go round, a (so-called) steam train, lots of others including a ferris wheel from which you can get a good idea of the Okazaki topography.
If you're worried about safety - have no fear - you're locked in and only the windows behind you are open a few centimtres. It doesn't take you long to work out why they've provided 2 little fans in each capsule. At 100 Yen a ride, go on indulge yourself! And in case you're worried about appearing like a child, you're spared that embarrassment as the ticket come via vending machines.
It's also a good place to get some exercise. Apart from the tennis and baseball, its a great place to do some serious walking.