Kalakkad-Mundanthurai is the largest protected area in Tamil Nadu — almost 900 square kilometres of evergreen and semi-evergreen forest rising into the Western Ghats from the dry plains around Tirunelveli. It is best known among naturalists for its endangered lion-tailed macaque population, but also holds tigers (though rarely seen), leopards, gaur, sloth bear, and the Nilgiri tahr at higher elevations.
The visitor infrastructure is limited. Entry is through Mundanthurai or Sengaltheri gates, both about an hour west of Tirunelveli, and there are simple forest rest houses for overnight stays — book through the Forest Department in Tirunelveli well in advance. Day visits along the Mundanthurai road and to the Servalar Dam are easy without a permit and give a good sense of the landscape.