Hyderabad, Feb. 27 -- Most people drive past the turnoff for Nagarjuna Sagar without realizing that they are just a boat ride away from India's own version of a sunken kingdom or "atlantis".

Beneath the wide, calm waters of the Krishna River reservoir lie the remains of Nagarjunakonda , a thriving ancient city that was submerged when the Nagarjuna Sagar Dam was built in the 1960s. What was once a valley filled with monasteries, learning centres and bustling life now rests underwater, hidden beneath the surface. Now, to experience what remains of this city, you have to take a 45-minute ferry ride into the middle of the reservoir to the island museum.

So, if you are looking for a weekend escape from Hyderabad that feels like stepping into...