Vadakkumnathan temple Thrissur is one of the oldest in South India. According to legends, it was founded by Lord Parasurama and enshrines Lord Shiva as the principal deity. The idol of Shiva, which is not visible, is covered under a mount of ghee, formed by the daily abhishekam (ablution) with ghee over the years. A devotee looking into the sanctum can now see only a sixteen-foot high mount of ghee embellished with thirteen cascading crescents of gold and three serpent hoods at top. According to traditional belief, this represents the snow-clad Mount Kailas, the abode of Parvathy and Parameswara. Shiva here is more popularly known as Vadakkunnathan (Sanskrit Vrishabhachala -Tamil Vidaikunrunathan Vidai - Vrishabha, kunru - chala ). Apart from Lord Shiva, Sree Parvathy, Sree Ganapathi, Lord Sankaranarayana and Sree Rama are enshrined within the nalambalam of the temple. Lord Vettekkaran (Siva in a hunter form) is also worshipped within the nalambalam enclosure.

Outside the nalambalam, there are shrines of Lord Krishna, Vrishabha, Parasurama, Simhodara, Dharmasastha and Adi Sankaracharya. Adi Sankara is believed to have been born to the Shivaguru-Aryamba couple of Kalady in answer to their prayers before Vadakkunnathan, as amsavatara of the Lord. Legend has it that Shiva appeared to both husband and wife in their dreams, and offered them a choice: a mediocre son who would live a long life, or an extraordinary son who would not live long. Both Shivaguru and Aryamba chose the latter. The son was named Shankara, in honour of Shiva.

The murals in the temple are known for its rarity and two of them - Vasukisayana and Nrithanatha - are even worshipped regularly. A fairly large white bullock on the verandah of the Nalambalam is worshipped as Nandikeswara. In the temple quadrangle, there are specified spots at which the devotees can offer their salutations to Lord Shiva of Kasi and Lord Chidambaranatha of Chidambaram, Lord of Shiva of Rameswaram, Sree Kali of Kodungallur, Urakam Ammathiruvadi, Lord Bharatha (Koodalmanickam) at Irinjalakuda, Sree Vyasa, Sree Hanuman and the serpent gods.

The temple theatre, known as koothambalam, has no parallel to cite anywhere else in the world. The four magnificent gateways called gopurams and the lofty masonry wall around the temple quadrangle are also imposing pieces of craftsmanship and skill. Ganapathi shrine is positioned facing the temple kitchen and offering of Appam (sweetened rice cake fried in ghee) to Mahaganapathy is one of the most important offerings at the temple. Propitiating Ganapathy here is believed to be a path to prosperity and wealth.