Kanchipuram
One of the 108 Divya Desams sacred to Vaishnavism, the Varadharaja Perumal Temple is the principal Vishnu temple of Kanchipuram — a complex of extraordinary scale with a beautiful 100-pillared hall and a unique 40-year ritual cycle in which the original stone deity (Atthi Varadar) is submerged in a temple tank for four decades and then revealed to the public for a brief 45-day window. If this window falls during your visit, witnessing it is considered among the most auspicious experiences in South Indian Hinduism.
The 100-pillared hall is a masterpiece of 14th-century Vijayanagara architecture — examine the columns closely for the extraordinary variety of sculpture. Priests in the outer corridors can explain the mythology if you engage them.