6 ounces raspberries, plus more for garnish (about 3/4 cup)
1 cup freshly squeezed lime juice (16 to 25 limes)
1 liter club soda
1 lime, thinly sliced, for serving
Add the sugar, raspberries and 1 cup water to a medium saucepan and bring to a simmer. Stir until the sugar dissolves. Press the berries with the back of a wooden spoon so their juices leach into the mixture. Let sit and steep until cool. Strain, discarding the solids.
Combine the cooled raspberry syrup, lime juice and club soda in a large pitcher. Pour into tall glasses filled with ice and garnish with the lime slices and a few extra berries.