Uttar Pradesh, a state in northern India, is the most populous state of the country and the most populous sub-national entity in the world. Two major rivers Ganga and Yamuna flow through the state and merge at Allahabad, forming a holy confluence. Uttar Pradesh was home to powerful empires of ancient and medieval India. The state has several historical, natural, and religious tourist destinations. The Taj Mahal, one of the seven wonders of the world, is located in Agra, Uttar Pradesh, which is also home to other exemplary Mughal architecture. Varanasi in Uttar Pradesh is the holiest pilgrim centre for Hindus, requiring a mandatory visit during one's lifetime. Kumbh Mela, a Hindu festival conducted in Allahabad once every 12 years, draws over 10 million pilgrims, resulting in one of the largest human gatherings in the world. Uttar Pradesh also has important Buddhist sites such as Sarnath and Kushi Nagar, which draw pilgrims from around the world.