Prime Minister Narendra Modi and school students ride on India's first underwater metro, in Kolkata on Wednesday. (Photo: The Independent/Yahoo news)

Built at a cost of nearly 600 million USD, the 4.8 kilometer section is part of India’s first underwater metro service, running under the Hooghly River.

The East-West corridor Metro line also has India’s deepest metro station at Howrah, 30 meters below ground level.