Nice photos. Long-shot, entrance-view and inside-temple view. It is 25th one in the 51 Shaktipeethas list (Savitri Sakthipith
, interesting to observe, it's called in your photo as Devikoop/ Bhadrakali).
I'm remembering the Saro mahatmya of Vamana purana, which depicts Sthaniswara mahima (content in telugu)
a lot. According to that, Sthaniswara is said to have been established by the prayers of Valakhilya Rishis after learning their mistakes in Sadhana. Lord Shiva appeared as Digambara
with Vishnu accompanying him as Mohini
. He taught a lesson to the Rishis that "no one can reach God with worldly thoughts". They misunderstood him and gave a curse that his Lingham will fall. The fallen Ligham with tremendous energy created massive out-breaks on earth. Finally they realized, the Digambara is no other than Lord Shiva, prąyed Ma Parvathi to bear the Lingham. She appeared in the form of Yoni and stabilized the Lingham as Panapattam, thus established Sthanu (The one who is stable and static). Sthanu sarovara present there is also very pious.