No offense intended to Vaishnavites please, but I recall reading somewhere that the Srirangam Temple in Trichy was, in ancient times, converted from an original Shiva temple on the same site. Apart from an old historical reference, the scholar's explanation mentioned that directly beneath the present inner sanctum, below ground level, there is a replicate inner sanctum ... and this concealed space, frequented only by the priesthood, was characteristic of a certain type of lingam installation evident elsewhere in India.
Can anyone provide further authoritative information to confirm or deny this?