Mangaladevi Temple, a 1000-year-old structure made of large granite pieces, is situated at an altitude of 1337 meters within the dense forests of the Periyar Tiger Reserve. The temple is dedicated to Mangaladevi, also known as Kannagi, a symbol of moral power as depicted in the Tamil epic, Silapathikaram, by Ilanko Adikal. The epic narrates how Kannagi avenged the wrongful death of her husband by burning down the town of Madurai. 

The temple architecture reflects the Pandyan style, and local lore suggests it was built by the Chera king Chenkuttuvan, with the installation ceremony attended by the Lankan king Gajabahu. Despite its current dilapidated state, the massive stones and boundary walls hint at its former grandeur. The temple complex includes four stone structures housing various idols, including Karuppa Swamy, Lord Shiva and Lord Ganapathy. 

Access to the temple is restricted to a 12-kilometer jeep ride through dense forests and high-altitude grasslands, starting from the northern boundary of the Periyar Tiger Reserve. The area around the temple is rich in biodiversity, including the endangered Nilgiri Tahr and unique orchid species, Habenaria periyarensis. The hillock location offers stunning views of the Western Ghats and the small villages of Tamil Nadu.

Visitors require prior permission from the Wildlife Warden at Thekkady, due to environmental protection measures. The temple opens to devotees only once a year during the Chithrapournami festival in April or May, when rituals are conducted by priests from Tamil Nadu and Kerala. The deity is adorned with flowers and silk, and devotees offer pongala, a sweet rice dish, as part of the celebrations.