This is a really nice drink made from the rhubarb that grows in the Mandala garden. We generally get plenty of rhubarb so don't be afraid to make a decently-sized batch (the first batch we made, we used double this recipe).
To server, dilute down in a 4:1 water:cordial ratio. For added kick, use carbonated water and maybe a shot of vodka.
Recipe taken from BBC Good Food
For around 600ml of cordial: