Kyu-Yasuda Garden

Kyu-Yasuda Garden (Kyu-Yasuda Teien, 旧安田庭園), a now-small Japanese stroll garden located in Ryogoku, was initially created as the garden of a suburban residence of a domain lord in around late 17th century.
It used to take in water from the neighboring Sumida River to enjoy the changes of scenery caused by the tide.
In 1889, it became in the possesion of Yasuda Zenjiro, founder of the Yasuda Financial Group. It was donated to then Tokyo City in 1922, so it was named Kyu-Yasuda Teien, which means "Former Yasuda Garden".
The garden doesn't take in the water from the Sumida River anymore, and the tide is artificially simulated by a water pump.
It's a 7-min walk from Ryogoku Station of the JR Sobu Line or Toei Oedo Line.

Noryo-no-yube

For two days in early August, an event called Noryo-no-yube, literally meaning "evening cool", is held in the evening (admission free). There will be traditional music performed and tea served on stages temporary built on the pond.

Kyu-Yasuda Garden is adjoining Yokoamicho Park. It's also close to Edo-Tokyo Museum.