The famous Mahamaham festival that takes place once in 12 years is linked closely with the town of Kumbakonam and the sacred tank located there. However, there are legends that associate this occasion with another holy place, Thirukkoshtiyur, situated in the Sivaganga district of Tamil Nadu.
Once, when the grand festival of Mahamaham came, King Puroorupa found himself engaged in the renovation work and service in the temple town of Thirukkoshtiyur. The king did not want to miss the sacred occasion and wished to take holy bath then. Lord Vishnu, who had taken abode at that place obliged his devotee and made holy Ganga flow out of the well that existed in the north-eastern part of the temple. The Lord also appeared in its midst and gave darshan to the king. Since then, this water body has come to be known as ‘Mahamaha Kinaru’, that is, ‘Mahamaha Well’. It has become a custom ever since for the deity of the temple to visit this sacred well riding on his Garuda mount during the Mahamaham festival, that happens once in twelve years.
Also, a unique worship takes place in the temple tank here during Masimaham, the annual festival that falls on the Maham star day during the Tamil month of Masi (February–March). This involves the lighting of the lamps on the banks of the Thirukkoshtiyur temple tank. Women who have got their specific wishes fulfilled will light a lamp on the banks of the tank on this Masimaham day, as an expression of their gratitude to the Lord. The ladies who make a wish in that year, will carry home those lamps, which they will light till the next year Masimaham. Once they too get what they want, they will bring those lamps to the temple tank on the subsequent Masimaham day and light the lamps on the banks of the tank. This worship is observed for the fulfillment of various desires related to marriage, getting progeny, poverty alleviation, getting employment, clearing of work-related problems etc.