I remember visiting London and marveling at the 14 different railway terminals surrounding the downtown core. As in other cities, this diversity of depots reflects the many different railway companies that ran "up" to the city (even today, British railway terminology refers to trains going "up" (to London) and "down" (from London).

Not all of the depots were large or imposing. Several were built by smaller railways and used primarily for local trains. The largest and busiest were, and remain today:

Paddington (the old Great Western route to the west of England);
Euston (the old London & North Western route to Birmingham, Manchester, Liverpool and Glasgow, today's busy West Coast Main Line);
St. Pancras (the Midland Railway route to the English Midlands that today is the terminus for the Channel Tunnel Rail Link high speed route to the European continent);
King's Cross (the terminus for the busy East Coast Main Line route to Newcastle, York, Edinburgh and, for all you Harry Potter fans, the Hogwarts School of Witchcraft and Wizardry);
Waterloo (Southern Railway trains to the south coast and, from 1994 to 2007, the terminus for high speed Eurostar services using the Channel Tunnel);
Victoria (more Southern railway services to the south coast, including the famous "boat trains" to Europe)