Rameshwaram at the extreme south of India is a centre of pilgrimage sacred to the Shiva and Vaishnava alike. It is at this point that Rama is believed to have launched his attack on Lanka.
After the conquest of Lanka, he is believed to have landed at Rameshwaram with Sita. The magnificent temple of Rameshwaram is dedicated to Shiva and Sita herself is fabled to have made the Lingam it enshrines.
A legend says that Rama, to purify himself of the sin committed in slaughtering the soldiers of Ravana, wished to worship a Lingam.
Hanuman was sent to get a Lingam from Benares but he got delayed and the auspicious occasion was passing hence Sita made a Lingam out of the seashore sand which Rama consecrated and worshipped.