This is a Jeevasamadhi of Azhukanni Siddhar.
There is a place to sit and meditate. You can go into meditative states here effortlessly.
How to get there
It is located inside the area of Kayarohana Swami Temple, 1 kms North West of Nagapattinam Junction Railway Station.
Map: https://goo.gl/maps/GarxrpibaYMQz6Sx9