Why's that there and where does it go?

A tunnel in Glasgow's financial district. Just sits there nestled amidst the sleek office blocks looking incongruous and intriguing.

I have a theory. I believe it to be the entrance into the Glaswegian version of Gringotts. Guarded not by wizened old goblins, but by pale nervous looking hooded folk hawking up great globules of phlegm at whoever dares to enter.

I don't dare. Intrigued as I am.