[arulpugazh]

2.2 miles is not really 'largest' isn't it

[chrismcb]

Is there a larger unused subway system?

[usr1106]

I guess Charleroi (Belgium) might have a longer one.

https://www.urbex.nl/metro-leger-charleroi-ligne-chatalet/

However, it's only 1 line that's unused, some other lines are in use.

[EamonnMR]

Perhaps the largest that happens to not be used.