While not exactly beautiful once you look a little closer, Enoshima is one of the Kanto region’s best-known and most convenient beach getaways. Just try not to swallow too much of the water.
The local sand contains a lot of volcanic minerals, giving a darker colour not to everyone’s taste. On the other hand that means that it absorbs the day’s sunlight and becomes a nice warming blanket in the spring when the water is icy. The beaches can be nicest in spring and early summer, before the infrastructure is built and the hordes of Tokyoites make their annual pilgrimage, flocking to the sand (though it’s game over for most swimmers on September 1st regardless of the weather).
Being mainly cliff-lined means not a lot of beach or swimming on the island (see below for the very notable exception) but it’s well worth a side-trip. As with many Japanese tourist draws it has a historical, religious significance: reflected in the presence of Enoshima Jinja (shrine). The shrine goes through three sections - Hetsunomiya, Nakatsunomya and Okutsunomiya - each with their own appeal, and is said to date back to at least 552 AD.
The standard itinerary is to trek up through the three shrines to the top viewpoint (only 20 minutes). The shopping street as you arrive has some nice, typically festive fare for a tourist site in Japan: barbecued squid on sticks, sticky rice sweets, etc. The Sky Candle, at the top is a high-tech lighthouse you can see for miles and miles, with a peaceful garden and top floor viewing platform.