Adam's Bridge: The Legendary Ocean Bridge:

The Indian Sanskrit epic Ramayana, written by Valmiki, describes a bridge called Setubandhanam that spans an ocean and connects Sri Lanka, the home of the deity Ravana, with India. According to the epic, Rama's monkey army helped him build the bridge as part of his efforts to reclaim his wife Sita by fighting Ravana.
According to the mythical epic, there once was a bridge—either man-made or natural—that connected Mannar Island, off the northwest coast of Sri Lanka, and Rameswaram Island, off the southeast coast of Tamil Nadu, India. According to geological data, this bridge was once a land bridge that connected Sri Lanka and India. It was constructed out of a chain of limestone shoals encircled by a shallow sea that ranges in depth from one to ten metres.

The thirty-kilometer bridge that spans the Palk Strait and the Gulf of Mannar was reputedly walkable until the fifteenth century, when storms caused the canal to deepen. Records from the Rameshwaram temple indicate that Rama's Bridge was entirely above sea level until a typhoon demolished it in the year 1480 AD.
An Abrahamic myth states that Adam used the bridge to reach a mountain, which the British named Adam's Peak, where he stood repentantly on one foot for a thousand years, leaving a large hollow mark resembling a footprint. This is the origin of the name "Adam's bridge" on the earliest map of the area, created in 1804.

In addition, the age of the bridge has been estimated to be between 3500 years old, which coincidentally is the age of the Ramayana.
"the age of Rama's bridge could only be 3,500 years" and that "the beaches' carbon dating roughly matches the dates of the Ramayana, so its link to the epic needs to be explored." It is important to remember, nevertheless, that the surveys that determined the bridge's age of 3,500 years were based on research done on corals that were grown on the bridge. Some have contended that this age simply indicates the age of the corals that were assessed. It has been determined that the bridge beneath the corals dates back hundreds of thousands of years.

Hindus revere Adam's Bridge and reject the Indian government's plan to dredge it to make Sethusamudram, a shipping canal, because of its association with the Rama legend and the belief that it was built by Lord Hanuman, the ape army, and Shri Rama and Shri Lakshman to reach Lanka and find Shri Rama's wife Sita, who had been abducted by Ravana.
The multi-million dollar Sethusamudram Shipping Canal Project was sanctioned by the Indian government in 2001. Its goal is to dredge the shallow ocean floor near Dhanushkodi in order to create a ship canal that will span the Palk Strait. It is anticipated that the channel will save the journey across Sri Lanka by more than 400 miles. The Hindu population in India strongly opposed the proposal to dredge through Rama's Bridge in order to maintain the current alignment of the proposed channel.

Defying the sentiment of Hindus Historians in Sri Lanka maintain that the bridge was a collapsible structure designed to traverse the sea and reach India as needed, but Sri Lankans believe that Ravana built the bridge himself using floating rocks that are composed of weightless corals.