Silent Valley, the 9000 hectare national park is believed to be the sole surviving bit of evergreen forest in the Sahya Ranges. It rises abruptly to the Nilgiri Plateau in the north and overlooks the plains of Mannarkkad in the south. The core of the Nilgiri Biosphere Reserve is the Silent Valley National Park. Despite its name, the Silent Valley (the clamour of Cicadas is conspicuously absent here) echoes with the sounds of teeming wildlife.
The denizens of this sprawling habitat of endangered virgin tropical forests include rare birds, deer and tiger.
Located in the Kundali Hills of the Western Ghats, the Silent Valley National Park holds a valuable reserve of rare plants and herbs. The park is rich in its wildlife, and elephants, lion-tailed macaques and tigers are the most common denizens of this park. A visit to this park should be considered a lifetime experience, as this is the last representative virgin tract of tropical evergreen forests in India. Perhaps, nowhere else can one also find such a representative collection of peninsular mammals, over a 100species of butterflies and 400 species of moths and other fauna like the Ceylon Frog Moth, Great Indian Hornbill, the Nilgiri Laughing Thrush and the Lion-tailed Macaque.
Vehicular transport is only up to Mukkali, nearly 24 km from the park. The rest of the way has to be covered on foot up to the source of Kunthipuzha, which flows through the valley before merging with the Bharathapuzha (Nila). There is huge, hollow tree in the park, which can hide at least 12 people in it.