Karasawayama Castle Ruins sit on a low mountain north of central Sano. The castle is gone, but the stonework, ridgeline paths, shrine precinct, and views over the Kanto Plain make the site feel substantial.
It is especially good in autumn, when the pines and maples soften the old defensive lines. The climb is not severe if you start from the upper approach, but wear shoes that can handle uneven ground.