Fill a glass with ice. Set aside.
Place a 1 inch piece of the rosemary in a cocktail shaker and muddle it slightly to break it up.
Fill the shaker with ice. Add blueberry syrup and grapefruit juice. Shake well.
Strain into your prepared glass. Top with club soda.
Garnish with a sprig of fresh rosemary, slice of grapefruit, and/or fresh blueberries.