Between the Ashinoko Skyline and Izu Skyline there is the route 20, also known as the Jukkoku Touge. This road actually starts in the hot spring town of Atami, climbs up to the mountain until the Izu Skyline north gate and then continues until Hakone Touge, where it is possible to enter the Ashinoko Skyline.
The section between the two Skyline routes is up in the mountains but as the 16 kilometer long road is twisting along the mountainside there is almost no elevation but there are a lot of corners. The scenery is also interesting, with views changing from grassy hills to far stretched view across the sea.
The road quality is generally very good and it is a toll-free route at the time of writing. There is a rest-stop parking with cablecar and observatory on the route as well. It is worth visiting as you can enjoy amazing panorama views on a clear day.
Google Maps location link:
Jukkoku Touge rest stop