Kamakhya Temple is regarded as one of the 51 Shakti Peethas. As per the legends, the genital organ (yoni) of Sati fell at this spot. Kamakhya Mandir is a natural cave with a spring. In order to reach the temple, one has to take a flight of steps that goes down into a dark and strange shrine. There is no concrete form of goddess inside the temple.

In the shrine, Kamakhya Devi, in the form of genital organ (yoni), presides as a big crevice in the bedrock. The Goddess is covered naturally by a rivulet of water gushing upward from an underground spring. The crevice is usually covered with sari, flowers and vermilion powder (Sindoor). The temple had been an ancient sacrificial site and till date, sacrifices are offered here. Every morning, group of devotees come to sacrifice goats.

The temple is very much ancient in its origin, yet it was restructured in 1665, when it was attacked by the Muslim invaders. The effort of this reconstruction was made by King Nar Narayan of Cooch, Bihar. The spire of this temple is shaped like a beehive. Besides Kamakhya Devi, there are images of Ganesha, Chamundeswari and various dancing sculptures. In the temple, an image of the King and related inscriptions are visible.

Source

http://www.culturalindia.net/indian-temples/kamakhya-devi-temple.html

http://www.templesofindia.net/content/kamakhya-temple-guwahati