Subramanya Shashti also known as Champa Shashti is celebrated honoring the birth of second son of Shiva named Subramanya / Skanda. It falls on the 6th day of the Hindu month of Marghashirsha, November-December in Gregorian calendar. This year (2015) it falls on 17th December.
He was born with a purpose to kill the demon Taraka. On this day devotees immerse themselves reading stories and sing Bhajans and Kirtans / Devotional songs of Lord Subramanya. The festivities start 6 days prior to the Shashti.
People worship the snake mound with great devotion. They worship the mound with all the pooja items and pour milk into the mound.
Palani in Tamil Nadu, Ghati Subramanya and Kukke Subramanya in Karnataka have two very popular and ancient temples dedicated to Lord Subramanya. Thousands throng this temple during this festival. Special pooja / prayers and rituals are held here.