The water bus ride is absolutely relaxing.

Be prepared for a child admission

Yes there is a fee - 300 yen. It has specific opening hours between about 9-4.30 pm. You can also have a tea ceremony in a tranquil setting.

My TFG guide sent this response: At HAMA RIKYU you can enjoy drinking green tea with sweets any time in the villa on the lake. If the person asking you informatin wants to see the tea ceremony(the process of making a cup of tea ), there is no performance at HAMA RIKYU. At KEIO PLAZA Hotel in SHINJUKU, you can experience tea ceremony every day. One hour with english explanation at 2000 yen. In the real tea house on tatami you can experience the tea ceremony fully. Rerervation is needed. Hope this helps! George

I was there in the afternoon and it was open. The park has a website but I think it is only in Japanese. My best guest is that it is open at least an hour later after the park opens. Enjoy this park, it is truly a lovely and manageable space to appreciate the Japanese garden aesthetic.

Hama Rikyu isn't all that big, and I'd agree it can be seen in an hour or so, unless you stop for tea in the tea-house on the pond. If gardens are your thing, there isn't much that's really great in Tokyo itself. I'd recommend Shinjuku Gyoen, to which you might want to allocate maybe 2 hours. Other options include Chinzanso (only need 20-30 minutes), the garden of the Nezu Museum (only 20 minutes, but the Museum itself is excellent), Gajoen (15 minutes), the garden of the New Otani Hotel (15 mins). I've always found the Imperial Palace gardens rather underwhelming. Not a garden, but Meiji Shrine is worth a visit, set in surprisingly deep woods in the centre of Tokyo. And Meguro Shizen Kyoikuen is more a nature reserve than a garden, but again worth visiting. Yoyogi Park is nice and spacious, and another favourite park of mine is Arisugawa Park, with its ornamental ponds, and hidden grove of plum trees. A lot of Tokyo's gardens are famous for one particular type of plant, and are stunning when that's in season, so do some research. For instance Shinjuku Gyoen is famous for late-flowering cherries, while Nezu Museum is famous for its irises. Kameido Tenjin Shrine has fabulous wisteria.

We liked it because of the ambience of the tea house in the middle of the man-made lagoon. As for the tea itself, they serve matcha green tea and provide a laminated set of instructions on the traditional, ceremonial way of drinking it. Don't expect food. :)