Ram Sethu is the alleged land bridge, more a causeway, connecting India to Lanka and believed to have been constructed by Lord Rama and his army at the time of the Ramayana.
Recent attempts to dredge a passage through it for ships has led to great controversy, during which the then UPA Government even submitted an affidavit in Court questioning the historicity of Lord Rama.
This matter is still to be satisfactorily settled and the various issues raised addressed properly.