Boil together the sugar and water until bubbling subsides and the edges begin to brown. Lower the heat and swirl gently as caramel turns brown. When an even light brown, remove from the heat, swirling, and let cool for two minutes.
Line a cookie sheet with parchment paper. Pour caramel in random shapes onto paper, and sprinkle with the walnuts. Let cool. When hardened, crack the candy with the back of a spoon.