Sri Vidyashankara Temple, Sringeri
This is one of the oldest temples in India, which dates back to 13th Century. The unique part of this temple is that there are twelve pillars which marks the twelve signs of the zodiac in their regular order, and they are arranged in such a manner that the rays of the sun fall on each of them in the order of the twelve solar months. Windows and doors along the temple walls are arranged such that equinoxes sunrise views reach the deity.
With these very reasons, it is one of the sacred and historic temples in South India