One of the few festivals that takes place in Japan during June is the Ajisai Matsuri (Hydrangea Festival). If you’re on your way to see the sights here (video) and make the most of the rainy season, you can take the shuttle bus (fare is included with admission) or hike a kilometer up to the falls. There are several gardens along the riverbank and a few shops and restaurants. You can walk along the road or follow a path next to the river among the flowers. The following photographs are some of the sights you might see along the way.
見帰りの滝—mikaeri no taki—Mikaeri Waterfall アジサイ(紫陽花)—ajisai—hydrangea あじさいまつり—ajisai matsuri—Hydrangea Festival
More info
Find out more about Mikaeri Falls.
http://youtu.be/8UnnpqdlfRM
If you read Japanese, here's the Hydrangea Festival website:
http://ouchi.fhl.ne.jp
For 2014, the festival is on from June 7-29.