The cities are habitable. There are “relics” of buildings but its a habitable zone. The bombs back then were airburst and released little fallout. Much of the Nagasaki blast was deflected because its a hilly area.
Pretty amazing when you think of the level of destruction from such small nuclear bombs. Couldn’t imagine what today’s weapons would do.
http://www.fantasticjapan.com/hiroshima-today.html