The old tunnel under the Elbe
In 1911, when this tunnel under the River Elbe in Hamburg was built, it was a technological sensation. And in many ways it still is today. The Alter Elbtunnel is 80ft below the surface, nearly 1,400ft long – and accessed by four giant elevators at each end. This would be cool enough if it was solely for pedestrians, but it isn't. It also takes cars.
Back then, workers at the local shipyards used the tunnel to get to and from work on the island of Steinwerder, sharing the tunnel with vehicles of all kinds. These days they (and everyone else) have other (faster) options, but you can still use the old Elbe tunnel for the sheer thrill of it. Just drive your car into one of the elevators, drive through the tunnel and ride another elevator up the other side.
The tunnel connects the city's St Pauli quarter and Steinwerder, where the exit offers a great view of Hamburg. It may seem inefficient by today's standards, but unless you're rushing to work at the shipyards (not very likely) it sounds like a cool way to pass your time in Hamburg. RM
Tunnel image (second from top): Andrew Sullivan