In my last travels to Japan, a friend took my husband and I to a place called Namja Town. She called it Food Disney. It is under the streets of Ikebukuro in Tokyo and is known for its Gyoza, ice cream, and desserts. But its more than just that. It's also a small discovery zone where you can find little hidden games and buttons to press. It's only 500 Yen to get in, and that's enough, because the passport is for big games that are in Japanese anyway. So enjoy the food, like Ice Cream town with weird flavors like Squid Ink or Tulip, and play around and have fun!
Namja Town Map (English)
Julie Gozali's Blog about Namja Town
(She mentions that the size was reduced for another small amusement park called J-World on a floor above! Built the year after our last visit I'm interested to check it out!)