Following the reproduction of an audio-mystery circle in the Tokyu Tamagawa train station by tracing the culture and nature of the Tamagawa basin at Artline Week 2007, Karesansui sounding reproduced the Suikan(the source of the Tamagawa River) by sound within the front lobby of the Ota-ward municiple office. Suikan is a bowl that has been carved by dripping water over a long period, and is somewhat like a Suikinkutsu created by nature. Water is collected in the Suikan, and once it overflows it creates a single drop of water. :::: expresses the dynamic scale of the process of a single water drop overflowing from the Suikan, then evolves from a small stream into a large river, which at the end reaches the ocean. The sound of the water drop, which was sampled at the source of the Tamagawa River at Mt. Kasatori, echoes through the entrance hall of the building by responding to the number of visitors crossing the threshold of the entrance hall. The sound of water is a symbol of people, and the sound of ripples will spread out by continuously dripping and accumulating. The more the people who visit the municiple office, the more the sound of ripples that richly spread out. The sound of nature that can be heard at the top of Mt. Kasatori and the movement of the sun is musically expressed in the area around this imaginary Suikan, and creates a rich soundscape.