India’s first underwater metro in Kolkata, an example of ‘Atmanirbhar Bharat’, is expected to be open for commuters by the end of 2023. The authorities have constructed a tunnel under the river Hooghly with an internal diameter of 5.55 meters and external diameters of 6.1 meters. Tunnels under the bed of river Hooghly, running 32 metres below water level, is considered to be an engineering marvel. The tunnel is 13 metres below the riverbed and 33 metres below ground level. The corridor passes below the river Hooghly between Mahakaran and Howrah Metro Station. This feature makes it the first underwater (Subaqueous tunnel) rail system under a major river in India.