A kamakura (no, not that Kamakura or that one, but this one) is a snow hut, a traditional type of shelter made by building and then hollowing out a mound of snow.
Since olden times, families in heavy-snowfall areas of Japan have built such snow domes, where they grill mochi, drink sake, and enjoy other treats.
In wintertime, many cities in "snow country" hold a kamakura festival, where groups of people gather to build veritable kamakura villages and enjoy various festivities.
There's a kamakura festival in Yokote City, Akita Prefecture. A little closer to Tokyo, there's the Kamakura Festival of Yunishigawa, a town said to have been founded by members of the Taira clan who fled there after their defeat at the hands of the Minamoto clan in the late 1100s.
The snow domes of Yunishikawa.