Srirangam, the most important pilgrim centre, surrounded by the waters of Kaveri and Kollidam, is an island town of 600 acres enclosed within the seven walls of Sri Ranganathaswamy temple. The rajagopuram, one of the 21 gopurams, with 72 mt height, 13 tiered, built in 1987, dominates the landscapes around for miles, while the other 20 gopurams are nearly six centuries old. Srirangam stands today as the biggest temple complex in India. This is a large, still functioning temple with courtyards withing courtyards - the outer ones containing shops and houses, the inner ones becoming more and more holy. The innermost level shelters the image of Vishnu in his aspect as Ranganatha, reclining on a serpent. This shrine is entered from the north, except on one day a year, on the festival of Vaikuntha Ekadasi, the north door is opened, and those who pass through acquire great merit.