Next day, on Monday (a national holiday), we got a beautiful sunny day and visited Osaka castle. It was very nice with nice view of yellow ginkgo tree leaves and magnificent castle. In addition, we came across a outdoor concert of Japanese taiko drums played by two high school teams. Their plays were quite nice and vibration of taiko sound stroke us pleasantly.
When we considered social events after the 12th ISDCI congress (in Fukuoka), Osaka and Kyoto may be a candidate for some after-conference tour, though it'll be in hot and humid summer.

The Japanese garden in Hei-An Jingu

Ginkgo trees in Osaka Castle Park

Osaka Castle Museum
Taiko Drum by a high school players in Osaka Castle Park