In my house, we used to celebrate Ganesh Chaturthi. Ganesh is the god of obstacles; he has a human body and an elephants head, with only one tusk. Initially, people used to do this in their homes. Then it became more of a community event, especially in Bombay. Small communities would get together and keep a deity of Ganesha and do prayers everyday and have events, like childrens programs and presentations and such. Its a 10 day event. You have to do it either for 10 days, 5 days, or 2.5 days. After praying every day, on the 10th day you take the deity to the sea and submerge it and let it go. Its called Visarjan. Every year, people would make these deities, from as small as an inch to as large as 100 feet tall. The deities were made from clay, they were made very beautifully. There are artists who make the statue of the deity Ganesha. Every day you would have prayers, and Prasad which is sweets prepared to offer to god and is shared with everyone.
In my moms house, they used to prepare for this by clearing the front room. They would go buy a deity and create a sort of alter and present it with silk garments and plants and lights and things. Every day, they would do the Pooja (prayer ceremony) in the morning. Generally the men in the family would do the Pooja, it was usually my moms father or one of her brothers or uncles, depending on who was there that day. Every day, after the Pooja they would have Aarti, which was a prayer after the Pooja. My grandmother would make Prasad every day. People who didnt have the deity in their home would come visit them and we would share the Prasad and food with them. On the 10th day, they would submerge the deity.
I havent ever been to the Ganesh Chaturthi festival in India. But, from what I have learned from Sunday School and from what I have read about or seen on TV, I know that the Ganesh Chaturti is a festival that is meant to honor Ganesh, as given by the name. But, I also know that it is a big deal in Bombay more than other parts of India. Thousands of people gather to take part in the Ganesh Chaturthi. When we did the Ganesh Chaturthi at my house, I dont remember it being that large of a deal, mainly because it takes a while to prepare and having to continue the same process for many days requires a decent amount of time that wasnt always readily available.
Annotation: This festival is documented in an article in the NewYork Times.
New York Times. Parade Caps Festival for a Hindu God. 30 August, 1997.