Ashigara is the region north of Hakone but there is no direct connection. Either it can be accessed via Gotemba or via Odawara. The mountains from Hakone continue into Ashigara. There is one road that passes from Minami-Ashigara to Gotemba over the mountain. It is the route 78 that merges into route 365 over the Ashigara Touge.
Starting from the route 78 in Minami-Ashigara, the road slowly climbs up to the mountain for the first. It is generally a faster section with long sweepers through slightly urban area. After 10-15 minutes, around 10 kilometer, there is a sudden turn to the right and from here road really starts to climb up onto the mountain. The road narrows down and there are several tight hairpins. This continues for around 1.5 kilometer after which the road becomes wider, and the next 1.5 kilometer is the best part of the route with superior asphalt quality and a nice variety of curves. It is worth driving this more than once.
Completing this fine piece of road lands you at the top of the Ashigara Touge, where there are several parkings scattered over a distance of a kilometer. It makes a good base for hiking adventures and views to either Shonan and Tokyo direction, or to Mount Fuji.
After the top, the road will descend down with wide lanes for the first part but after around 1 kilometer there is an exit to left towards Gotemba. This road is very narrow and does not give any scenic views as it passes straight through forest. The route 365, which is direction if you just keep following the road, is also not the widest road but it is wide enough for cars to pass each other and has some scenic views, including a parking area with view spot.
This route 365 has some tight hairpins in the middle section and will afterwards slowly curve down towards the north of Gotemba, first passing a Golf country club. A bit later you will face oncoming traffic of the Tomei highway as the road goes down past the Tomei highway and a few moments later passing under it.
The Ashigara Touge route can be driven almost year round but is prone to nature damage so road closure might happen. Also take care for branches and fallen rocks on the road after heavy wind and/or rainfall.
Google Maps link:
Ashigara Touge