I’m interested in what happens beneath the surface of things. How do machines work? Where do subterranean rivers flow? What’s the origin of a word? Why do men behave as they do? My nine-year-old son shares an interest in things unseen, most evidently in his fascination with Berlin’s U-Bahn system. When we first moved to the city he persuaded me to travel with him on all nine underground lines. He opened carriage doors at most of the network’s 170 stations. At school he advised his teachers on the easiest way to reach unfamiliar stops. He even taught himself to recognise the different models of U-Bahn by the sound of their motors, identifying an approaching train before it reaches the platform.
At U Deutsche Oper my son and I clambered off the platform and went walkabout, in the care of half-a-dozen BVG guides. With families, couples and not-a-single-trainspotter, we explored a little-used branch line which connects the U2 and U7 (with the electricity switched off to the third rail). A guide took my son’s hand and explained signal and power systems, enlightening us into the meaning of blue tunnel lights, and transported him to a kind of subterranean heaven.
At present the BVG, the public transport operator Berliner Verkehrsbetriebe, has suspended the Tunnelwanderung. On offer instead is a fascinating midnight tunnel tour, with participants towed through 35 kilometres of tunnels by a Akkulok locomotive on open flatcars. It's not a walk, but what a ride.