On the border of Gunma and Nagano Prefectures, about 4km east of Karuizawa on Rte 18, you'll find the Usui Pass, historically an important point on the Nakasendō, one of the two routes of the Edo period that linked Tokyo and Kyoto. A train line ran through the pass from 1893 to 1997. The observation platform has stunning views of Asama-yama and surrounding mountains. There's no public transport; for directions, ask at the Karuizawa Tourist Association office.