There are a few peaceful spots in Tokyo where you can escape the buzz and the rush of the city. Mejiro Japanese gardens is one of them. Entrance is free and you can walk around gazing at the waters and taking in the calm surroundings.
The gardens proved a great picnic spot, even in the rain you can shelter under the hexagon gazebo and watch the ducks and carp.
The gardens are open every day 9am - 5pm,longer in the summer months (closed 2nd & 4th Mondays) . There are illuminations in the Autumn time too!
Website (Japanese) - https://www.city.toshima.lg.jp/kusei/kusei/midori_kankyo/midori_hiroba/000869.html
Address - 3-20-18 Mejiro, Toshima-ku, Tokyo (5 minutes walk from Mejiro Station)