Kamakura would be good for a day trip. Here is a good way to do it.

Take the JR Tokaido Line down to Ofuna Stn. Then take the JR Yokotsuka Line to Kamakura Stn. From here take the Enoden (Enoshima Densha) to Enoshima. This is an old electrified narrow gauge that snakes thru neighborhoods and along shoreline. Then from Enoshima take the Shonan Monorail back to Ofuna Stn. This is a hanging monorail vs the Monorail to Haneda that rides the rail. Here are some places to go along the way.

1. There are several temples near the Kita-Kamakura Stn. within walking distance.
2. Near the Kamakura Stn., just to the north at the end of the main street is a large temple with a large ponds. It will be full of lotus leaves in the summer. Many nice small restaurants for lunch near the temple. The walking street along the main street is full of little shops.
3. The Daibutsu (Big Buddha) is on the Enoden Hase Stn. about 15-20 minutes walk north.
4. The Enoshima beach will be busy with people in the summer and tranquil in the winter.
5. There are places for dinner near the Ofuna Stn. from expensive restaurants on the front street to 100yen sushi shops on back streets.