Though Hinduism has two main branches : Shaivism and Vaishnavism, they both belong to the Sanatana Dharma (the perennial religion). Adi Guru Shankaracharya went across the length and breadth of India and established four peethas (seats of learning) - Badrinath, Dwarka, Jagannath Puri and Kanchi.
The line of Shankaracharyas is still extant. During the Maha Kumbh festival held at Prayag every 12 years, saints and shankaracharyas from all parts of India congregate to offer their prayers from Makar Sankranti right up till Maha Shiv Ratri.
Srimad Bhagavad Gita, as spoken by Lord Krishna to the Maharabharata warrior Arjuna, is considered the holiest of the holy books in Hindu religion.