From Wikipedia:
Dhanushkodi has the only land border between India and Sri Lanka which is one of the smallest in the world-just 50 yards in length on a shoal in Palk Strait. Before the 1964 cyclone, Dhanushkodi was a flourishing tourist and pilgrimage town. Since Ceylon (now Sri Lanka) is just 19 miles (31 km) away, there were many ferry services between Dhanushkodi and Talaimannar of Ceylon, transporting travellers and goods across the sea. There were hotels, textile shops and dharmashalas catering to these pilgrims and travellers. The Railway line to Dhanushkodi–which did not touch Rameshwaram then and destroyed in the 1964 cyclone-went directly from Mandapam to Dhanushkodi. Dhanushkodi in those days had a railway station, a small railway hospital, a higher secondary school, a post office, customs and port offices etc.
All that remains today are the ruins of what once was a town.