I am going to say,
Waterloo train station as it is an architecturally sound beacon to the London Underground, which opened in 1863 and the beginning of the 150 year exploration into the world of mass transit.
This has to be something which changed the world. And built the world we know.
Its not just the old, this station has been about since the 1850's and yet still is at the forefront of transport hubs in the world connecting two of the worlds greatest capitals via train and a tunnel under the sea. (London - Paris) A hub to all London Boroughs with a new tube link being built as we speak, the Crossrail. And direct connections to Heathrow airport, the worlds busiest airport. One of the only places in the world where you could truly disappear, train plane or automobile this place connects you to it all.
This symbolizes mass transit, and a notion which a nation teaches, that the world is not such a vast space, it brings us all together as England did with the railway, this extension, this monument to the bridging of old and new.
The Revolution has begun