The Kangra Valley Railway is the least known of the 5 “recognized” mountain railways of the Indian Railways. Numerous videos can be seen on Youtube. If you are not familiar with the basics, you can see:
It may or may not be converted to BG. It is unlike the other lines to Shimla, Darjeeling, Udhagamandalam and Matheran in that it was not built primarily to serve a hill station, but to facilitate movement of equipment to be used in the construction of a hydro-electric power station. This was known as the Shanan Power House. Some distance beyond the terminus of Joginder Nagar, there is a funicular railway (known by various other names such as a winch railway) which provided a means for shifting heavy machinery up a steep slope. The entire route of the funicular railway is not in working condition, but the first two legs from Joginder Nagar are still working as shown in the video.
The terminus at Joginder Nagar:
This is the end of the line for the two pairs of passenger trains from Pathankot (most of the passenger trains terminate earlier at Baijnath Paprola). The line reaches a point where goods (including heavy equipment for the project) can be transferred to the funicular railway (which is part of the electricity board or whoever runs the hydel project) but is assuredly NOT part of the Indian Railways.
You will see this sign at the bottom:
All technical details can be seen here. However, as of today, the line if functional only up to Winch Camp, the end of section B. It appears that no special permission is needed for outsiders to travel on this section, which is 1.45 +2.0 = 3.45 km long and climbs from 4133 ft to 7990 ft.
This would presumably make it longer than the better-known funicular at the Palani temple in Tamil Nadu. This trip is summarized in this video (in Hindi with English subtitles):
So now you know what the Kangra Valley line was built for. Admittedly, it also serves minor hill stations like Dalhousie and Dharmasala besides religious centres such as Jawalamukhi.
The ownership of the Shanan Power House is a bit complex. It is situated in Himachal Pradesh but is the property of the Punjab State Electricity Board, who are due to transfer it to their counterparts in HP by 2024.But it is gradually getting run down and may not operate for long: