Membrane complete, scaffolding removed, online ticket sales started: since 6 December, the test tower has finally left the construction site phase behind.

The transition from the construction phase to complete operation open to visitors is marked by other news: here, on the test tower website, with immediate effect those interested can also book tickets for their visit to Germany's highest outdoor viewing platform. Until now, tickets were only available on site at the box office; now, admission tickets can be purchased in advance very conveniently, also for weekends in the future.

Tower Manager Michael Klein gives a positive summary after the brilliant start to the visitors' platform: "Since 13 October, approximately 25,000 visitors have used the outdoor viewing platform. There were record numbers of visitors during fine weather and on public holidays: on 1 November alone, 2385 guests enjoyed the view." Whether the opening hours you can see on this page will be extended in future, what events can take place at a height of 232 metres, are matters he deliberately left open: "We are taking a long-term approach to such questions." There is no blueprint and no role model for operation open to visitors on the roof of a research facility for high-speed elevators: other thyssenkrupp test towers are purely test towers - without public access. And: without an artistic membrane. The Rottweil model is unique.

Of course the journalists want to know whether there were disputes during construction, or about who perhaps lost their nerve during this megaproject and whether project manager Hardy Stimmer is still annoyed at the fact there was a delay of a few months with the membrane. "No," he replies emphatically. "An engineer understands when great challenges have to be faced in other groups involved in the construction." He stressed that the artistically twisted membrane made of 17,000 square metres of material has never been constructed in this form anywhere in the world. For its attachment in the first place, an assembly platform had to be conceived, built and then tested by the appropriate notified body. "This takes time," says Stimmer, "and everyonecan understand that." The strong winds in which the industrial climbers were unable to work up on the tower also contributed to the time delays. "Safety has the highest priority for thyssenkrupp," says Hardy Stimmer, "and I am glad to say that there has not been a single accident on this construction site." Klaus Strohmeier of the general contractor Züblin agrees with the thyssenkrupp project manager: "We always had our eye on the result - with a unique building like this, nothing can ruin our mood."

For Hardy Stimmer, pride, joy and melancholy come together on this day: "Rottweil has become dear to my heart," he says. He knows the tower like nobody else, saw it growing, and must soon say farewell to "his" project. When the parking spaces have been set out and plants and trees have been placed in the areas around the tower - "also depending on the weather" - most people are unlikely to remember the hot construction phase. Until then, however, Hardy Stimmer still has a few clearing up tasks to complete. Long after the journalists have left and darkness has set in, he can still be seen sitting at his desk in the brightly lit building site container.