This is an adit to the tailrace tunnel, part of the abandoned and unfinished Loharinag-Pala Hydro Power Project on the Bhagtrathi river (one of the headstreams of the Ganges river).
View photo inside this tunnel.
View photo of the end of this tunnel, which is flooded.
For more info about the Loharinag-Pala Hydro Power Project, read en.wikipedia.org/wiki/Loharinag_Pala_Hydro_Power_Project.