The Hario radio towers

Three concrete towers, 136 metres tall, finished in 1922 for the Imperial Navy and still standing because they were built too well to demolish cheaply. The signal that told the fleet to proceed with the attack on Pearl Harbor is generally understood to have been relayed from here.

The three Hario towers are reinforced concrete masts, each about 136 m tall with a 38 m circumference, standing in an equilateral triangle about 300 m apart. The Imperial Navy built them in 1922 as a long-wave radio transmitting station, and the buildings were designated National Important Cultural Properties in March 2013. They are also part of the Japan Heritage story of the naval district at Sasebo. A secondary article says the station stayed in use until 1997.

There is a well-known story that the Pearl Harbor signal 'Niitakayama nobore 1208' was sent from here. The Japanese Wikipedia article says that is not certain and that it was most likely sent from other stations. What is certain is the scale: three towers, each about 136 m tall, with volunteer guides from the Hario Radio Tower Preservation Society and part of the site open since 2013.

The catch is that it only works from Uragashira. From Miura it is about 25 minutes each way and roughly ¥15,600 in taxi fares, and the site closes for an hour at midday. There is little here beyond the towers, so it suits people who like industrial history more than scenery. Skip it if your ship is at Miura and you are short of time.