Shonan is the coastal area thirty to sixty minutes south of Tokyo-Yokohama. Shonan is a part of Sagami Bay (see map above). The bay does extend beyond the confines of Hiratsuka and Hayama, but the surrounding areas are less populated than this central part.
There are a mixture of sandy and rocky beaches here. During the summer, as you might expect being so close to Tokyo-Yokohama, the beaches are quite crowded. The beaches of central Kamakura (Zaimokuza) and Fujisawa near Enoshima (Island) seem to be the most popular destinations. The long stretches of beach between Fujisawa and Hiratsuka woluld be the least crowded during the summer.
South of Zushi-Hayama, the coast becomes rocky; there are several popular diving spots in this area. Sandy beaches resume on the southern and eastern sides of the Miura Peninsula in Miura and Yokosuka.
Hiratsuka is the western end of Shonan. When traveling from Tokyo, it begins to feel like the country here. Tanabata is a very big festival held in Hiratsuka every July 7th.
Kamakura is the most famous city in Shonan. It was the capital of Japan about 700 years ago. It has many famous temples, nice beaches, and forested hills. The Kamakura Daibutsu (Big Buddha) is perhaps the single most photographed object in Japan.
Zushi is a residential community with a fair-sized beach and some interesting history. Between Zushi and Hayama is the newly discovered Nagae-Sakurayama Kofun -- two ancient keyhole-shaped burial mounds -- 1700 years old and big enough to hold several houses each!
Hayama is quite hilly and green with several beaches -- some sandy -- some good for snorkeling and diving. It is home to quite a few artists and non-Japanese. The Emperor also has a Imperial retreat here.