Trial runs are underway on the challenging western portion of the Kolkata Metro’s East-West corridor, a 520-m stretch of which passes under the Hooghly. This is the country’s first underwater transport tunnel, and the corridor will significantly improve commuting on one of the city’s most congested stretches

https://indianexpress.com/article/explained/metro-under-the-river-hooghly-river-kmrc-howrah-maidan-8569520/