Ooty (Udhagamandalam) is Tamil Nadu's most famous hill station, at 2,240 metres in the Nilgiri Hills, 90 km northeast of Coimbatore. The British established it as the summer capital of the Madras Presidency in the early 19th century, and it retains something of that heritage in its cottages, botanical gardens, and cool air — though it's now crowded and commercially developed in ways the colonial administrators would not recognise.
The Nilgiri Mountain Railway, a UNESCO World Heritage Site, is the best way to arrive. The narrow-gauge rack-and-pinion line from Mettupalayam (near Coimbatore) to Ooty climbs 2,000 metres through tea estates, eucalyptus forests, and Toda villages in about five hours. The steam-hauled section from Mettupalayam to Coonoor is one of the most spectacular train journeys in India.
The Government Botanical Garden, laid out in 1848, is a pleasant place to walk. Ooty Lake is surrounded by hire boats and pedal cycles — pleasant on weekdays, heaving on weekends. The surrounding Nilgiri Hills offer better experiences: Dodda Betta (the highest peak at 2,637 metres) has walking trails, and the tea estates around Coonoor (18 km south and less touristy than Ooty) produce some of the best Nilgiri black tea in India.
The best time to visit is April to June when the hills are green after rain and the days are cool and clear. Avoid school holidays (April/May) if you dislike crowds.