The Nilgiri, often referred to as the Nilgiri Hills, are a range of mountains with at least 24 peaks above 2,000 metres (6,600 ft), in the westernmost part of Tamil Nadu state at the junction of Karnataka and Kerala states in Southern India. They are part of the larger Western Ghats mountain chain making up the southwestern edge of the Deccan Plateau.
The hills are separated from the Karnataka plateau to the north by the Moyar River and from the Anaimalai Hills and Palni Hills to the south by the Palghat Gap. The Nilgiris District of Tamil Nadu lies within these mountains.
The Western Ghats, Nilgiri Sub-Cluster (6,000+ sq km), including all of Mukurthi National Park in the south-eastern corner of the Nilgiris, is under consideration by the UNESCO World Heritage Committee for selection as a World Heritage Site.The Nilgiri Biosphere Reserve, which includes the Nilgiri Hills, is part of the UNESCO World Network of Biosphere Reserves.
The highest waterfall, Kolakambai Fall, north of Kolakambai hill, has an unbroken fall of 400 feet (120 m). Nearby is the 150 feet (46 m) Halashana falls Second is Catherine Falls, near Kotagiri, with a 250-foot (76 m) fall, named after the wife of M.D. Cockburn, believed to have introduced coffee plantations to the Nilgiri Hills. The Upper and Lower Pykara falls have falls of 180 feet (55 m), and 200 feet (61 m), respectively. The 170 feet (52 m) Kalhutti Fall is off the Segur Peak. The Karteri Fall, near Aruvankadu had the first power station which supplied the original Cordite Factory with electricity. Law's Fall, near Coonoor, is interesting due to its association with the engineer Major G. C. Law who supervised building of the Coonoor Ghat road.
Over 2700 species of flowering plants, 160 species of fern and fern allies, countless types of flowerless plants, mosses, fungi, algae, land lichens are found in the sholas of the Nilgiris. No other Hill station has so many exotic species.Much of the Nilgiris natural Montane grasslands and shrublands interspersed with sholas has been much disturbed or destroyed by extensive tea plantations, easy motor vehicle access and extensive commercial planting and harvesting of non-native eucalyptus and wattle plantations (Acacia dealbata, Acacia mearnsii and cattle grazing. In addition there is one large, and several smaller hydro-electric impoundments in the area. Scotch broom has become an ecologically damaging invasive species.
The Nilgiri hills can be reached by the Nilgiri Mountain Railway and by motor vehicle over five separate Nilgiri Ghat Roads.The best trekking seasons are April–June and September–December. Application for trekking permits should be made in advance with the Wildlife warden.The Tour of Nilgiris is a week-long annual bicycling tour that traverses the Nilgiris mountains with the twin objectives of exploring the Nilgiris while promoting cycling as an eco-friendly mode of transport and leisure.