What is the most northern city?

The line was originally named the Great Northern & City Railway, and was intended to allow mainline trains of the Great Northern Railway to run from Finsbury Park directly into the City of London at Moorgate. Accordingly, the tubes were made large enough to take a main-line train, unlike those of the other tube railways being built in London at the time. However, the Great Northern was lukewarm about the scheme, and the GN&CR had to settle for a northern terminus in tube underneath Finsbury Park station. The line opened in 1904. It was originally electrified with an unusual fourth-rail system featuring a conductor rail outside each running rail. This was altered to the standard LT arrangement at a later date.