A quiet kayaking trip (take your own kayak or packraft) around the bends of this lush river, leading up to an amazing tunnel. This tunnel was man-made around 400 years ago to divert the stream for the cultivation of rice at that time. The river is a popular spot for Bass fishing. Small motor boats can be hired (fishing license required), however boats cannot enter the area with the tunnel.

Located in the Boso Peninsula Chiba, just over 1 hour from central Tokyo by car via the Tokyo Bay Aqua Line. Also accessible by train (Kazusa-Kameyama Station) within 3 hours from central Tokyo.