Knackebrod, or crispbread, has been part of the Swedish diet since antiquity. It is said that the Vikings ate the nutty rye flour cracker: It's nutritious and nearly unperishable. Traditionally, it is baked with a center hole for drying on a wooden pole, and its grooves, which help it cook evenly, are created by a stud-covered rolling pin. Swedes eat crispbread often, but it's especially popular on Midsummer's Eve paired with pickled herring and a shot of strong drink.