The Cucumber Cooler isn't a classic cocktail. It's not even very well known, but for those who are familiar with it (or those who've ever enjoyed one at the end of a sweltering summer's day) will attest, it's just the ticket to for a sundowner in the garden. Or the balcony. Or looking out the window wishing you had a balcony.
To make the rosemary syrup add water sugar and rosemary sprigs in a pan and gently heat. Let it stew and lightly simmer for 15 minutes. Once cooled, strain into a bottle or jar and store in the fridge. It'll last for a couple of weeks.
If you do not have a juicer, muddle the cucumber in a tin with all the other ingredients and then shake. It's not the same as it's a lot boozier overall, but it works quite nicely in an all-together different way.