The Nilachal type refers to a type of Hindu temple architecture in Assam, a state in Northeast India that is characterized by a bulbous polygonal dome built over a cruciform ratha type bada.

This hybrid style was first developed in the Kamakhya temple on the Nilachal hills under the Koch kingdom of Assam and became popular as a style later under the Ahom kingdom of Assam. The Nilachal Hill or Kamagiri hill which is situated at a distance of 7 km from Guwahati, the capital city of Assam, is of great historical, archeological as well as religious importance. The Nilachal Hill in Assam which was earlier believed to be a sacrificial site for the ‘Khasis’, now has a group of ancient temples on the top, the most eminent of them being the Kamakhya temple. The temple of Goddess Shakti or Kamakhya temple is the oldest and most revered centre for Shakti worship which led to the spread of the Tantrik Hinduism sect. It is believed that the female genitalia (yoni) of dead Sati fell down while her corpse was being carried by her husband Shiva which turned the hill blue, therefore the name Neelachal (Blue Spread) or Nilachal Hill.

There is no image of Shakti here. At a corner of a cave in the temple, there is a sculptured image of the Yoni of the Goddess, which is the object of reverence. A natural spring in the area keeps the stone moist. Other temples on the Nilachal hill include those of Tara, Bhairavi, Bhuvaneswari and Ghantakarna. Durga Puja is celebrated at Nilachal hill annually during Navratri in the month of September- October. It is a three day long festival which attracts several visitors. A unique festival that is also observed here is the Ambuvaci (Ameti) fertility festival wherein it is believed that the Goddess (mother Earth) undergoes her menstrual period. During this period the temple at Nilachal hill is closed for three days and opened with great festivity on the fourth day. It is believed to be inauspicious to till the ground or to plant seeds, during this three day period.