The Nilgiri Mountain Railway (NMR) connects the town of Mettupalayam with the hill station of Udagamandalam (Ooty), in the Nilgiri Hills of southern India. Both towns are in the state of Tamil Nadu. It is the only rack railway in India, and uses the Abt system.The Nilgiri Mountain railway is one of the oldest mountain railways in India. Under consideration since 1845, the line was finally opened by the British in 1899, and was initially operated by the Madras Railway Company. The railway is one of the few in the world dependent on steam locomotives.
The Southern Railway India, in Tamil Nadu which operates the NMR, incurs an annual shortfall of Rs 4 crores, (~1 million USD). During the Centenary celebrations of Nilgiri Mountain Railway in 1999 Railway Minister Nitish Kumar announced that the line would soon be electrified.
In July 2005, UNESCO added the Nilgiri Mountain Railway as an extension to the World Heritage Site of Darjeeling Himalayan Railway, the site then became known as "Mountain Railways of India." after it satisfied the necessary criteria, thus forcing abandonment of modernisation plans.

The NMR track is 1,000 mm (3 ft 3+3⁄8 in) gauge and the railway is isolated from other narrow gauge lines.Between Mettupalayam and Coonoor, the line uses the rack and pinion system to climb the steep gradient. On this rack section trains are operated by 'X' Class steam rack locomotives manufactured by the Swiss Locomotive and Machine Works of Winterthur in Switzerland. These steam locomotives can be used on any part of the line (either with or without the rack section), but the newer diesel locomotives can only operate on the upper section, between Coonoor and Udagamandalam. The steam locomotives are always marshalled at the downhill (Mettupalayam) end of the train. The average gradient in this rack section is 1 in 24.5, with a maximum of 1 in 12. Between Coonoor and Udagamandalam the train is operated by a YDM4 diesel locomotive using conventional rail adhesion principles. On this section the locomotive is always at the Coonoor end of the train as although the line is not steep enough to need a rack rail, the ruling gradient out of Coonoor is still very steep at 1 in 25.
As of 2007, there is one train a day over the rack section, which starts from Mettupalayam at 07:10 reaches Ooty at noon. The return train starts from Ooty at 15:00, and reaches Mettupalayam at 18:35. The train is scheduled to connect to the Nilgiri Express, which travels from Mettupalayam to Chennai. A summer special service is also run during the months of April and May, starting from Mettupalayam at 09:30 and from Ooty at 12:15. Between Coonoor and Udagamandalam there are four daily trains each way.

NMR issues old style tickets, keeping in line with the World Heritage Site status.
Even though the NMR stations have networked computerised ticketing systems for onward journeys, it still issues old style manual tickets for the Ooty-Mettupalayam journey to preserve the World Heritage Site status of the railway. However, Ticket booking is similar to other conventional trains and can also be done via the Indian Railways' website. It is advisable to book tickets for this railway in advance, especially during peak season.
The majority of repairs to the locomotives are carried out at the Coonoor shed but many of the steam locomotives have been rebuilt at the Golden Rock Workshops. Carriages are repaired at Mettupalayam but, like the locomotives, are taken to one of the big railway workshops for major work. Due to its popularity, a number of passengers using the NMR have requested that the Southern Railways should covert the section from Coonoor to Udagamandalam to steam locomotive,extending the present steam traction between Mettupalayam and Coonoor

The train covers a distance of 46 km (28 miles), travels through 208 curves, 16 tunnels, and 250 bridges. The uphill journey takes around 290 minutes (4.8 hours), and the downhill journey takes 215 minutes (3.6 hours)

An excited crowd receives the Nilgiri Mountain Train at the Ooty station
Mettupalayam - 0 km, 1069ft above sea level - Junction with the Broad Gauge line from Coimbatore. Passengers cross the platform to the Nilgiri train. There is a small locomotive shed here and the carriage workshops for the line.
Leaving Mettupalayum, the line is adhesion worked and actually drops for a short distance before crossing the River Bhavaani, after which it starts to climb gently.
Kallar - 8 km, 1260ft - Closed as a passenger station, this is where the rack rail begins. As the train leaves the station, the gradient is 1 in 12.
Adderly - 13 km, 2390ft - Closed as a passenger station but is still a water stop.

Journey by the NMR provides spectacular views of the Nilgiri Hills
Hillgrove - 18 km, 3580ft - Block post and water stop, also has refreshments for passengers.
Runneymede - 21 km, 4612ft - Closed as a passenger station but is still a water stop.
Kateri Road - 25 km, 5070ft - Closed as a passenger station, trains do not stop here.
Coonoor - 28 km, 5616ft - main intermediate station on the line at site of the locomotive workshops as well as the top end of the rack rail. Trains must reverse a short distance before continuing their climb to Ooty. It is normal for the locomotive to be changed here with diesel traction, being normal for all trains to Ooty.
Wellington - 29 km, 5804ft
Aruvankadu - 32 km, 6144ft
Ketti - 38 km, 6864ft
Lovedale - 42 km, 7694ft

The Lovedale railway station
From a short distance before Lovedale, the line descends into Ooty.
Ooty- 46 km, 7228ft (2200 m).