What is the religious significance of Kartik Purnima?

Kartik Purnima holds multiple layers of significance: it marks Lord Shiva’s victory over the triple cities of the demons (Tripurasura Vadha), the conclusion of Chaturmas (the four sacred months of the rains), the Kartik Snan (a holy bath believed to wash away the sins of a lifetime), and the Guru Nanak Jayanti in the Sikh tradition. In Varanasi, it is also the conclusion of the five-day Ganga Mahotsav cultural festival.