PM Modi recently inaugurated India's first underwater metro line in Kolkata, marking a major leap forward in the country's infrastructure
Image: @BJP4India/X
The Kolkata Metro extension, featuring the Howrah Maidan-Esplanade Metro section, includes the first transportation tunnel in India to pass under a major river
Image: PTI
Here are other cities in the world featuring underwater train and metro systems
Image: ANI
Thames Tunnel is believed to be the oldest underwater rail tunnel, crossing the Thames in London
Image: @atlantean526/X
Hong Kong's Mass Transit Railway (MTR) system has four underwater railway tunnels that carry trains under Victoria Harbour
Image: @atila_pg/X
The Marmaray Tunnel, a 13.5 km long undersea railway tunnel in Istanbul connects the city's Asian and European sides
Image: @RLeighTurner/X
The Seikan Tunnel is a 53.85 km dual-gauge railway tunnel in Japan, with a 23.3 km portion under the seabed of the Tsugaru Strait
Image: @japan/X
The Transbay Tube is an underwater rail tunnel between the cities of San Francisco and Oakland in California
Image: @jachristian/X
The Channel Tunnel is an undersea rail tunnel that runs beneath the English Channel and links southern England and northern France
Image: @rossmackenzie/X
Bangabandhu Sheikh Mujibur Rahman Tunnel is an underwater expressway tunnel in the port city of Chittagong, Bangladesh under the Karnaphuli river