Between Karuizawa and Yokokawa is a historic road called the Nakasendo. Long before cars existed it used to be trade route between Tokyo and Kyoto. Nowadays it is mountain road which is mainly used for sightseeing traffic. But is an amazing driving road for the person that loves the twisties.
Corners, that is what this road has plentiful. In total there are 184 corners, on a stretch of only 12 kilometer. It are mainly tight, low speed corners with the occasional straight section. From Yokokawa towards Karuizawa the road has a slight upwards gradient. The asphalt quality is very good and generally the road is very wide, making it a perfect driving road.
Along the Nakasendo road are also the remains of an old train route. A lot of old tunnels and bridges, which the most recognizable spot being the Megane-bashi. Nowadays the old train route has become a walking route so you can also go up some of the bridges and through some of the tunnels by foot. There are two parkings along the Nakasendo road which make good stopping areas in case you plan to a bit of walking along this old historic road. Beware of bears and other wild animals.
On the Yokokawa part of the Nakasendo is also a small lake called Usui lake. It has a parking and is a good leisure spot for a walk or to enjoy fishing. Certainly head over here if you like Autumn colors as these are very beautiful in this area.
Google Maps location link:
Usui Touge Nakasendo road