Thukalassery Mahadeva temple is located on the northern side of Manimalayar near Thiruvalla in Pathanamthitta district, Kerala. The Shiva temple is atop a small hill. The Shivling worshipped in the temple is known as Rakshasa Lingam.
The darshanam of Thukalassery Mahadeva is towards east. The upa devatas worshipped in the temple are Sree Krishna, Nagam, Aryayakkal Bhagavathy and two murtis of Vishnu Bhagavan.
The 8-day annual festival begins with kodiyettam on Uthrattathi nakshatra in Kumbham month.
As per history, the temple belonged in ancient times to Thukalan who was a Naduvazhi (local ruler) and hence the name Thukalassery. The temple was managed by Tharayil Kuzhikkattu, Thekkedath Kuzhikkattu, Parambooru and Mulavana - all Tantri families (priests).
Currently, the temple is managed by Mahadevar Kshetra Haindava Seva Samiti.