The Shree Padmanabhaswamy Temple dedicated to Lord Vishnu was constructed in 8th century CE according to historians. This temple is built in the Chera & Dravidian style of architecture which is very unique in Kerala and neighbouring states, as the construction was done keeping the local weather and wind direction in mind.

The present structure was built in the 18th century by the then Travancore Maharaja Marthanda Varma.

The massive temple structure has a staggering 100 feet high "Gopuram", the main temple tower. Padmananbhaswamy's massive idol measures 18 feet in length and is covered with gold and other precious stones. The Deity is visible through three doors. Padmanabha or Vishnu reclining on the serpent Anantha or Adi Sesha is the center of the Padmanabhaswamy temple. With his right hand placed over a Shiva lingam, Vishnu is flanked by Lakshmi, the goddess of prosperity and Bhudevi, the goddess of Earth. Bramha is shown to emanate from Vishnu’s navel. Interestingly, the image of Vishnu is made out of 12,000 shaligrams or fossilized shells that can be traced back to the banks of Nepal’s Gandaki River. 

Padmanabhaswamy temple is also considered as the world's richest temple. This temple is renowned for its beauty and grandeur. The royal family of Travancore owns the temple treasure after a nine-year-long legal battle in the Supreme Court. Mobile phones along with all electronic items are banned inside the temple premises and No photography is allowed. The entry to the temple is free. 

Foreigners & Non Hindus are not allowed inside the temple. Only Hindus are permitted inside the temple. The dress code for men is Mund / Dhoti with or without Angavastra. Men need to wear mundu or dhoti (worn around the waist and going down up to the heels) and should not wear shirts of any kind. Women has to wear a saree or have to wear dhothi / mund over their dresses.

Anyone can access more information about this temple on https://en.wikipedia.org/wiki/Padmanabhaswamy_Temple

The foundation of the present gopuram was laid in 1566. The temple has a corridor with 365 and one-quarter sculptured granite-stone pillars with elaborate carvings which stands out to be an ultimate testimonial for the Vishwakarma sthapathis in sculpting this architectural masterpiece. This corridor extends from the eastern side into the sanctum sanctorum. An 80-foot (24 m) flagstaff stands in front of the main entry from the prakaram(closed precincts of a temple). The ground floor under the gopuram (main entrance in the eastern side) is known as the 'Nataka Sala' where the famous temple art Kathakali was staged in the night during the ten-day uthsavam (festival) conducted twice a year, during the Malayalam months of Meenam and Thulam.

The platforms in front of the vimanam and where the deity rests are both carved out of a single massive stone and hence called "Ottakkal-mandapam". On the orders of Marthanda Varma (1706–58), the Ottakkal-mandapam was cut out of a rock at Thirumala, about 4 miles (6.4 km) north of the temple. It measured 20 square feet (1.9 m2; 190 dm2; 19,000 cm2) in area by 2.5 feet (30 in; 7.6 dm; 76 cm) thick and was placed in front of the deity in the month of Edavom 906 M.E. (1731 CE). At the same time, Marthanda Varma also brought 12,000 shaligrams, aniconic representations of Vishnu, from the Gandaki River, north of Benares (now known as Varanasi) to the temple. These were used in the reconsecration of the Padmanabha.

Several extant Hindu Texts like the Vishnu Purana, Brahma Purana, Matsya Purana, Varaha Purana, Skanda Purana, Padma Purana, Vayu Purana, Bhagavata Purana etc mention the Padmanabhaswamy Temple.