If you visit Rameshwaram it is not rare to see there the floating stones which were used to built the bridge to Lanka by Hanuman and his army to serve the Lord Rama.
Some temples will have it in small wells inside the shrine, you can find it in Rama teertham and Hanukan temple.
Also, if you go to Dhanurkoti (Dhanuh - bow, koti - end), the very end of the main land which was the point where bridge started, you can find temple there on the way with these stones.
Don’t miss the opportunity to get wet in 22 wells in the main temple of Rameshwaram - where Sita and Rama lived after returning from Lanka. Holy waters in the hot day refresh you from within and whithout!!