Kamakura is located south of Tokyo, and can be reached easily. It is mostly famous for all of its Buddhist Zen temples and Shinto shrines. Prepare with a good set of shoes if you plan to do a more thorough visit of them as you will have to walk a lot, both distance wise as well as up and down the small hills. Kamakura is also famous for a large bronze buddha (13m high). It may be nice to have a look at, but if you have visit the big Buddha in Ushiku, this Buddha feels quite modest.
During the spring, this is a very good place to see the cherry blossom, and during the early summer, it is a popular place for flower viewing.
If you have time and like to spend some time trekking, there are quite a number of good hiking trails in the area. It is not always obvious how to find them, so make sure you before hand look up the different trails and how to find the starting point.
If you on the other hand do not like to walk, Kamakura is also a good place to just relax down by the beach.