Ram setu is first noted in valmiki Ramayana, Its Godly men -ape man made bridge between India and Sri Lanka. This bridge is actually link of shallow limestone rocks. Ram Setu or Adam Bridge is 18 miles (30 KM) long between Gulf of Mannar and Palk strait.
WikiPedia Says : “It was reportedly passable on foot up to the 15th century until storms deepened the channel: temple records seem to say that Rama’s Bridge was completely above sea level until it broke in a cyclone in 1480 CE”. Ram Setu – Adams bridge in Google Maps Images as follows: