Approximately 10 km north of Notsuke Peninsula meanders the Po River. In the river basin is a series of crater-like hollows. These are sites of pit dwellings from ancient times. There are over 4,400 hollows, which form the “Shibetsu Prehistoric Sites”, the largest group of pit dwellings in Japan. People lived at these prehistoric sites continuously from 10,000 years ago up until the 17th century. When the sites were excavated, large amounts of salmon bones were unearthed from the pit dwellings that span every era. This conveys the history of the long symbiosis with nature and the people who gathered here every autumn in search of the salmon.