Oyu Stone Circles
The Oyu site consists of two circles that are now separated by a modern highway. The circles were constructed from river stones at the beginning of the Late Jomon period (2000 BC). "Nonakado" (lower right circle) measures 42 meters (138 ft) in diameter; the slightly larger "Manza" (upper left circle) is 46 meters (151 ft) in diameter, making it the largest stone circle in Japan.
An imaginary line joining the centers of the two circles would point NW to the summer solstice and SE to the winter solistice.