Casuarina Beach which is in Karainagar, Jaffna District about 20 kilometers from Jaffna of Northern Province. It used to be a popular tourist destination, but tourist numbers have declined due to Sri Lankan Civil War. However after the end of the 3 decade long war, the beaches unspoilt location has led to a growing number of visitors.
Season From March Till November.
http://en.m.wikipedia.org/wiki/List_of_beaches_in_Sri_Lanka#Beruwala