I was told about this drink by many a Spanish student during my TEFL years and we finally got to taste it (by the pint load!) on a trip to the Basque country many, many years ago. It has been a staple of our summer beverages since - especially good by the pool on hot days or serving during World Cup matches (cheering for or against Spain - both work!).
1 part red table wine
1 part coca cola
Lots of ice
Coca Cola is the recommended cola, Pepsi would be too sweet and the biggest tip here is not to use a good red wine but the plonkiest of plonk you have left sitting on your wine rack.