Inside the temple compound is a large damp footprint pressed into the granite floor, water seeping into it continually from a spring beneath the rock. The footprint is said to be Sita's, left when she was held briefly here on her way to Lanka, and the water is regarded as sacred — pilgrims dab it on their foreheads.
The geology probably explains it perfectly well: a natural fissure in the granite outcrop carrying ground water to the surface, the depression worn into a vaguely foot-shaped basin by centuries of feet and hands. But the legend is the better story, and you may want to wait a few minutes after a tour group leaves to see the print in quiet.