Ottasekharamangalam Mahadeva temple is located at Ottasekharamangalam on the Kattakada – Chembur – Vellara road in Thiruvananthapuram district, Kerala. The annual festival begins on Chathayam nakshatra in Dhanu Masam and ends on Thiruvathira Nakshatra.
The three karas of the region brings three flag posts and the flags are installed in there of them by the Tantri of the temple.
There are two temples dedicated to Shiva and one Vishnu in the shrine. All the three deities are the main murtis in the temple.
In the center is Shiva as fierce Aghora murti. This murti was consecrated by Khara Maharishi. This Shiva was so fierce that it was impossible to perform pujas or enter the shrine. To lessen the ferocity of the Aghora Shiva another Shiva shrine was built known as Thekkedam temple. Some strength of Aghora Shiva was transferred into the new Shiva temple.
The Vishnu in the temple is considered to be Mohini Avatar. It is believed that the temple was built in 1915 AD during the renovation of the temple. The Mohini murti was earlier worshipped in Thengmanmadam. It is said that the original Tantri of the shrine disagreed to install the Vishnu murti in the shrine. So the Tantri was replaced by Nelluvelil as Tantri. He installed the Mohini murti as four-armed Vishnu.
All the three temples in the shrine have Vatta Sreekovil or round sanctum sanctorum. All the deities face east. The Chittar River flows behind the temple.
The Upa Devatas in the temple are Ganapathy, Sastha, Yakshi, Naga and Saptamatrikas.