Morning: Visit the UNESCO World Heritage Site of Shore Temple, Arjuna's Penance, and Five Rathas. Take a stroll at the stunning Mahabalipuram Beach.
Afternoon: Explore the Tiger Cave, a rock-cut Hindu temple. Head to the Krishna's Butterball, a massive rock balanced on a hill slope. Visit the Mahishamardini Cave, a rock-cut temple dedicated to Lord Shiva.
Evening: Watch the Light and Sound Show at the Shore Temple describing the ancient history of the place.
Morning: Take a ride on the famous Nilgiri Mountain Railway to Ooty. Visit the Government Botanical Garden, spread over 55 acres with rare trees, shrubs and flowers.
Afternoon: Visit Doddabetta Peak, the highest peak in the Nilgiri Mountains offering a panoramic view of the valleys around. Explore the Tea Museum to learn about the history and production of tea in the region.
Evening: Take a walk around the Ooty Lake and enjoy boating. Visit the St. Stephen's Church, a Gothic-style church built-in 1820 by the British East India Company.
Other places to consider are the Auroville City, the Matrimandir, and the Chunnambar Boat House in Pondicherry. In Ooty, you can visit the Avalanche Lake, Pykara Waterfall, and the Wax World Museum.
For a side trip, you can visit Coonoor, a nearby hill station known for its tea plantations and trekking trails.
To maximize your fun, try the local cuisine like Dosa, Idli, Sambar, and Rasam. Don't forget to buy some homemade chocolates from Ooty.
Lastly, keep your camera ready to capture the stunning views of the Nilgiri Mountains.