Up until the 15th century, you could apparently walk from India to Sri Lanka. Rama’s Bridge is a short chain of limestone islands and shoals with a very fraught religious and political history.
The ocean is extremely shallow here, and as recently as the 1400s the entire link was supposedly above water. That makes it pretty much impossible for ships to get from one side to the other; they have to go around Sri Lanka instead. The Indian government has proposed dredging this area so that ships can pass through, but there are many environmental and religious objections to this plan.
Religious? Well, some Islamic sources hold that Adam (of Adam and Eve fame) fell to earth in Sri Lanka and crossed over to the continent via this bridge – hence the alternative name Adam’s Bridge. The Hindu epic Ramayana holds that the god Rama created the bridge so that his army of monkey-men could cross into Sri Lanka. Fundamentalists in India have suggested that the bridge is not natural at all but man-made (by Rama), and it has become a bit of a flashpoint for political debate in India.