While not necessarily being one of the most famous places in Tokyo, Hamarikyu Gardens certainly give you an excellent environment to go for a walk, relax, and enjoy nature.
Located in Chuo-ku, this 250,165 m² landscaped garden surrounds the Shioiri Pond, in the middle of which visitors can enjoy matcha and Japanese sweets in a traditional teahouse. The garden is accessible through its two Northern Gates or through the Tokyo Cruise Ship (water bus) that departs from Asakusa.
It really feels like an oasis in the middle of so many tall buildings. I really recommend you to visit!
