A whole 33 meter deep!
https://indianexpress.com/article/lifestyle/destination-of-the-week/kolkata-howrah-metro-station-deepest-station-first-underwater-metro-tunnel-7894783/
"Commuters coming from suburbs and various districts will be able to reach Salt Lake in a very short time. This has been unthinkable so far," Rupayan Mitra, Public Relations Officer, Kolkata Metro Rail said
https://indianexpress.com/article/lifestyle/destination-of-the-week/kolkata-howrah-metro-station-deepest-station-first-underwater-metro-tunnel-7894783/
Howrah metro station, the deepest station in the country, expected to be operational by 2023
indianexpress.com"Commuters coming from suburbs and various districts will be able to reach Salt Lake in a very short time. This has been unthinkable so far," Rupayan Mitra, Public Relations Officer, Kolkata Metro Rail said