Route 134 and the Enoden train line run along Sagami Bay and command a really beautiful sea view. I think the best point to wait for the sun set is at Inamura-ga-saki Park; the second best is between the two stations of Kamakura Kokomae and Insmura-ga-saki on the Enoden Line. The sun sets over Enoshima Island and Mt. Fuji, and leaves us with a nice afterglow. Check sunset times from here.
Caution: Route 134 almost always has heavy traffic in the evening, so you probably won’t want to drive.