Dug deep and found this photo of the old Elbe Tunnel, one of the oldest operating tunnels in Europe. It runs beneath a river and connects the city of Hamburg to the port/shipyards at Steinwerder. Interestingly, traffic only flows in one direction the first half of the day and reverses in the second half.
You can take a walk down a winding set of stairs to reach the pedestrian paths in the tunnel or join some cars and bicycles in manually operated lifts that takes you underground (or under-river, in this case).
Taken with a Canon 650D and 18-135mm kit lens
Check out my other SPC 24 entry:
Beyond what the eyes can see
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