is Gozan no Okuribi everyear august 16th?I believe that this festival is fixed on the 16th. Nailing down the dates for festivals can be difficult, some set their dates as a specific date on the Gregorian Calendar (what we use), and other festival will use the Lunar Calendar, which uses the Chinese new year as the first day of the year (I think). Others will use "The second weekend in August", or some rule like that. The weirdest one I have come across so far is the Kanda Festival in Tokyo, which only happens on Odd years, and occurs on the closest Saturday and Sunday to the May 15th May 15th last year was on a Wednesday, which makes the Saturday equidistant. It was held on the 11th and 12th.
Is everything clear?
Some places that have Traditional festivals have switched from the Lunar Calendar to the Gregorian. So... some cities (Hirastuka near Tokyo) will celebrate Tanabata (7th day of the 7th month of the Lunar Calendar) in July, and other cities (Kyoto, Sendai) will celebrate it in August.
Is it clear as mud yet?
That said, you will have to check and re-check. I have found that the Seasonal Traditions Website will copy the dates from the previous year, and the correct when they find out that the dates have changed. One way that I use to figure out the date is to look for a history of when the festival was held over the last few years, and make a prediction from that.
You seem to be trying to get traditional summer events in Japan that people enjoy. One such event is a trip to the beach. There is a hot springs resort town called Atami that is near Tokyo that may interest you. It used to have the three largest geysers in the world, but ground shifting many years ago has altered the water supply to the geyser. Atami is south of Mount Fuji, has a Shinkansen station, and is on the coast between Tokyo and Nagoya. There are lots of resorts and onsens that you can stay at, and many have open air baths. The one I stayed at had the open air bath on the roof of the resort. There is a beach to go to, the Modern Museum of art, a cultural center that has Geisha Dances every Sunday, and fireworks in the harbor. When I went this year in July, the resort had roped off an area in the harbor for it's guests to watch the fireworks. Here is this year link to the dates of the fireworks:
http://www.goldenjipangu.com/140412atami.htmlAnd here is a older link, that has information about what to do in Atami:
http://www.atamispa.com/atami_ex/english/sightseeing/index.htmThis link has the fireworks schedule from a few years ago, and gives you an idea of how the dates can change. The castle may still contain dolls, but the exhibit I saw had to do with Optical Illusions.
As for the best Onsen Experience, I am giving you a link to Uji's top nine list. In terms of information on this website, Uji is very good, and in Uji I trust:
http://www.japan-guide.com/forum/quereadisplay.html?0+94500My personal favorite hot spring to go is the hotel Urashima at Kii-Katsuura. This is a seaside town near Natchi Taisha that has a Fishing fleet. The hotel has two open air hot springs baths, that are located in seacaves. You sit in the bath, looking out over the ocean, and can listen to the waves crash on the rocks below the cave. The buffet meal at the hotel also has a Sushi carving demonstration, which usually starts with a 3-4 foot long fresh Tuna. This place is about a 4 hour train ride south of Osaka. The hotel is in the background of the photo of the fishing fleet on this link:
http://www.japan-guide.com/e/e4956.htmlKii-Katsurra is also close to Shirahama which is one of the three large hot springs beach resort towns, along with Atami, and Beppu.
