''Bonalu'', a grand Hindu festival of Telangana dedicated to Goddess ''Mahakali''

Bonalu,  a contraction of the  Sanskrit word ''Bhojanam'' or ''Bojan'', is an annual Hindu Festival quite popular in the twin cities of  Hyderabad and Secunderabad and, other parts of Telangana state, South India.  Celebrated during  Ashada Masam that falls in July/August this festival is dedicated to Mahakali who is being worshipped, particularly by women folks.  It involves worship of Kali in her various forms such  Ankalamma, Maremma,  Pochamma, Yellamma, Pedamma etc.  The highlight of this festive event is  conducting special poojas  for goddess Yellamma during the first and last day of the festival. Offering of naivaidhyam - food (Bonam in  Telugu means meal) is a sacred ritual  and this event  is symbolic of expressing gratitude to the goddess after fulfilment of vows taken before. 

Bonalu'' a Hindu festival of Telangana state, India, soundcloud.com

Above image: A woman carrying cooked food in a decorated pot  with neem leaves to be offered to the goddess Mahakali at the temple.

A woman carrying Bonam, Telangana. .nativeplanet.com

Women carrying Bonam (cooked meal) to the temple.andhrawishesh.com/

A special meal is cooked  at home by   women after observing certain religious norms such as taking bath in the early mooring, wearing clean dress and offering prayer, etc.,  before cooking. Taking non-vegetarian during  this period  is a taboo. This is also true of menfolk.  Likewise women experiencing ''Period'' are not allowed to participate in the function. Nor are they allowed to get into the temple. 

The special meal meant for the goddess is cooked in a new earthen or brass pot which is decorated with neem leaves (neem leaves have medicinal properties and the neem tree is often associated with Paraskthi), turmeric and vermilion, Once Bonam is prepared by mixing rice along with milk and jaggery (country  sugar) it is time for the women to head toward the temple.  Normally, they carry the pot with cooked food on their head to the temple and  reverentially make the offering to the deity along with bangles and sarees. The tradition has it offering should be made with bangles and sarees, preferably yellow in color. Devotees also offer Thottelu - made of color papers.  

Brass idol of Mahakali. .amazon.in

Young girls carrying Bonam en.etemaaddaily.com/

As to the origin of this festival, it all began when this  region was in the grip of Cholera (gattara in Telugu). When the soldiers in the military  went to Ujjaini, Madhya Pradesh  on duty from here, they prayed at the  Ujjaini Mahakali temple to save the people of Hyderabad and Secundeabad from the dangerous disease. Their prayer got a positive result and upon their return, the soldiers led by one Appaiah had a wooden idol of Ujjaini Mahakali installed in Secundrabad. This annual festival began during that period  to convey the gratitude of the people to the goddess for having saved tens of thousands of people from the epidemic in the past and for her continuous protection. 

Women carrying Bonalu (food), Telangana. timescontent.com

There are many Mahakali temples in both cities and devotees throng the temples on that day by carrying the Bonam on the head and wearing traditional dress. Normally during the first Sunday of Aashaadam, celebrations begin at Golconda Fort followed by Ujjaini Mahakali Temple in Secunderabad and Balkampet. During the procession, many women will go into a trance - a sort of hypnotic state as if they were possessed by spirits  and the crowds will pour water on them  and on their feet to pacify them. Pothuraju dances to the beat of drums are common in some place.  Pothuraju is supposedly the brother of Kali who is bare bodied and well-built wearing red-colored dhoti. 

Yet another feature is priests carrying ghatam (pot) from the first day of the festival to the last day. It is made of copper decorated with the image of the goddess. Smearing turmeric paste all over his body, the priest will carry the ghatam with devotion. On the final day it will be immersed in the water body. 

https://www.telanganatourism.gov.in/partials/about/festivals-of-telangana/bonalu.html

https://en.wikipedia.org/wiki/Bonalu

https://www.thehindu.com/news/cities/Hyderabad/a-city-shaped-and-reshaped-by-epidemics/article31085592.ece