Nemuro and the Northern Territories
I went to Nemuro to satisfy my personal desire of reaching every possible geographical landmark.
The Nosappu cape, near Nemuro, is the easternmost point of Japan, but it wouldn't be so if the Northern Territories were not under Russian jurisdiction.
The Northern Territories is a group of islands off Hokkaido's coast, known in Japanese as the Habomai group. They were occupied by the Soviet Union after WWII, and are claimed by Japan until the present date.
The area in dispute is more than twice that of Okinawa prefecture (but the weather isn't that nice!)