Berlin fintech start-up Number26 is named after the number of cubes that make up a Rubik’s cube. Only by coincidence does it reside at Unter den Linden 26.

The old imperial avenue, linking the Prussian royal palace and the Brandenburg Gate, is the heart of the German capital, yet Valentin Stalf, the Austrian co-founder of the real-time mobile banking service, says: "This place is great value for money."