Kamakura was the capital of Japan during the Kamakura shogunate, from 1185 to 1333.
Kamakura is now mainly known for its temples and shrines. Kotoku-in, with the monumental outdoor bronze statue of Amida Buddha, is the most famous of these.
Kamakura is just a little too big to cover on foot, but a network of buses radiates out from the train station. Kotokuin and Hasedera can also be reached by taking the Enoden line three stops out to Hase station.
Nevertheless, for the energetic ones, there is a nice hike starting from the Tokeiji and ending near the Kotokuin. You will walk, with some climbing, through forest. The hike also passes through Zeniarai Benten Shrine, if you are curious about the money washing ceremony. The hike takes about 3 hours, if you also stop and visit the temples along the way. Even in Summer, the shade on the path manages to keep the temperature bearable (you still are in Japan in Summer, anyway!). If you are on a day-trip, doing the hike of course limits a bit the chances of visiting some of the less reachable temples.