Digging London's Newest Tunnel

London's $25 billion public transit project (Europe's largest) is now halfway done. Crossrail, a 73-mile addition to the city's rail network, will connect Heathrow airport to Essex, adding an estimated 10 percent in ridership capacity.

Witnessing workers and machines build massive tunnels 80 feet underground since 2009 has been an interesting sight on its own. But the project also ended up being quite the archeological opportunity. An incredible range of remains -- from an ancient Roman road to graves of Black Death victims -- have been unearthed.