The Vandiyur Mariamman Teppakulam is a huge square temple tank — roughly 300 metres on a side — with a small island shrine at its centre. The tank dates to the 17th century and was excavated to supply the bricks used in the construction of the Thirumalai Nayak Palace nearby.
Most of the year the tank is dry and used for cricket matches by neighbourhood kids. In the Tamil month of Thai (January-February) it is flooded for the floating festival (Teppam), when illuminated processional floats carry the temple's deities around the island by night. If you can time your visit to the festival, do.