Reading books together with dad in the evening is an enjoyable activity that uplifts and nourishes everyone's minds. This is such a nice way to spend time with each other. Series like The Little House books or The Chronicles of Narnia are especially good choices for their appeal to a broad range of ages. Series also provide the added benefits of building familiarity and allows practice in sustaining attention and concentration on characters as they are followed from one book to another. We spent one enjoyable evening have each of my girls act out the latter poem.
Exercise is another way to battle cabin fever.
I have found exercise videos palatable enough to use, because I can stay at home and choose the best time for our family. Another advantage is that special equipment is not generally needed. The children can join in, too, which develops good habits in them and also burns off some pent-up energy. An occasional break in routine is a good antidote to the doldrums. This can help us return to concentrate more fully on the schooling later.