Pondicherry (Puducherry) is a Union Territory on the Bay of Bengal, 160 km south of Chennai. The French controlled it from 1674 to 1954, and the French quarter around the seafront — the White Town — survives largely intact: yellow colonial buildings, tree-lined streets named after French officers, a promenade along the seafront, and a neighbourhood where you can eat a genuinely good crêpe. It's a small, walkable area and quite unlike anywhere else in south India.
The Sri Aurobindo Ashram, founded by the philosopher-yogi Sri Aurobindo in 1926, remains the spiritual heart of the town. The Ashram has a large following and the town attracts seekers and residents from around the world. Auroville, the experimental international township 10 km north, was founded by the Ashram's co-founder Mirra Alfassa ('The Mother') in 1968 and now has around 3,000 residents from 60 countries. The Matrimandir — a large golden dome at its centre intended for meditation — can be visited with prior registration.
The seafront promenade (Rock Beach) is popular for morning and evening walks. The beaches at Pondicherry itself are not suitable for swimming due to currents and pollution, but Auroville beach to the north is better.
Pondicherry is easy from Chennai by bus (3 hours) or via the suburban rail to Villupuram and then bus. It's a logical stop on the coastal route between Chennai and Thanjavur.