Anandhapadmanabha Swamy is a lesser known one of the 108 Divya Desams dedicated to the Hindu deity Vishnu. It dates back roughly to the late eighth or early ninth century AD. The temple is known for two rock cut temples, one dedicated to Shiva and the other to Vishnu. There is a huge underground behind the 6th room. It is directly connected to kings palace.
References
Anantha Padmanabha Swamy Temple Wikipedia(Text) CC BY-SA