Combine sugar, honey, water and salt in a large heavy skillet. Place over medium-high heat and cook, stirring occasionally, until the mixture turns golden, 3 to 4 minutes. Add walnuts, reduce heat to medium-low and cook, stirring, until deep golden brown, 2 to 3 minutes more. Turn the mixture out on the prepared baking sheet, spreading in an even layer. When completely cooled, break into clusters.