At a minor tram stop in the small city of Heilbronn in southwest Germany, the ticket machine is so sophisticated that you can tap in “London” as your destination and get details of all the tram and train connections necessary to get you from a random location in Baden-Württemberg to St Pancras. Yet from the traveller’s point of view, that is not the most amazing thing about this city.

I visited Heilbronn this week after its selection as European Green Capital 2027. The judges rewarded its moves towards more sustainable mobility, including autonomous motoring, and the use of noise management to improve the city's appeal. Heilbronn sparkled in the late autumn sunshine, so I called in at the tourist office for advice on the highlights. A helpful staff member handed me a map and identified the usual German suspects: handsome Rathaus (town hall); imposing cathedral; leafy riverside walk. Then she pointed out a tower – and said: “If you want to visit the Hafenmarktturm, we can lend you the key.”

Now, I have encountered a few locations deep in the UK countryside where the gentleman in the Old Rectory can unlock the village church on demand. But in Heilbronn the tower offer is nothing short of self-service tourism – allowing you literally to unlock a city landmark. I duly filled out a rather solemn official form and handed over a €20 note as a key deposit. “Lock the gate behind you, or everyone will follow you in,” my new friend added as I headed for the door.

Perhaps I should get out more, but this was the most fun I have had all year. The Hafenmarktturm soars above the Old Town, a study in red sandstone to match the deepening afternoon. As the newly appointed keeper of the key, I unlocked the gate to a spiral walkway, closed it carefully behind me, and ascended to the viewing platform on a succession of implausibly antiquated staircases. The thinking seems to be: we have a handsome sandstone tower that provides superb city views. But Heilbronn is neither Paris nor Dubai, so rather than having somebody in attendance in case the odd tourist shows up, why don’t we just allow visitors to let themselves in?

In many parts of the world, the health-and-safety police would intervene. But I salute a city that allows visitors to clamber through its monuments unaccompanied. This was not the first time I have peered over a handsome Old Town as the sun called it a day, but it was easily the most memorable: with a shiver of joy, I felt for a moment like a character in Wim Wenders’ Cold War masterpiece Wings of Desire. I celebrated the glorious solitude of altitude – and the self-timer on modern smartphones.

Other locations should follow suit. I’m not suggesting that the Eiffel Tower staff should all take the day off and let tourists borrow the keys and make their own fun. Self-service tourism would be a hard sell at the Louvre, now with slightly fewer treasures than it used to have. Yet could a British market town be brave enough to let visitors rummage unsupervised through its heritage? I hope so. Meanwhile, come to Heilbronn. Borrow the key. Explore to your heart’s content.

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Tower of power: You can be in control during a visit to Heilbronn, western Germany

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