Plotted on TeleGeography's Internet Exchange Map are the buildings that connect the cables of the whole 'net. It's a really good picture of what the infrastructure of the entire internet looks like.
The map gives information on 274 internet exchanges and 512 buildings. Click a specific pin to find out more information about that exchange. It's interesting to see how concentrated these high-tech spots are in Europe for example, yet how sparse they are in Northern Africa. If you wanted to destroy the entire online world, this map would be a good starting point. [InternetExchangeMap via Telegeography — h/t @ajblum]