Under Elschner's management, the 1920s witnessed the Excelsior transformed into a hotel complex. Using contemporary deluxe US hotels as inspiration, Elschner installed new power and water systems and gas heating, and the coal-powered bakery and kitchens were introduced to electricity. Between 1925 and 1926, the hotel's guest capacity was expanded under the guidance of architects Heidenreich und Michel. In 1927-28, under the direction of architect
Johann Emil Schaudt (1871–1957), an 1800 m² area of the hotel cellars was transformed into a
spa. In 1929, an underpass connecting the hotel with the Anhalter Bahnhof across the street was constructed. The 80-metre long, 3-metre wide and 3-metre high 1.2 million
Reichsmark construction, is believed to have been the largest of its type in the world. The tunnel meant that the hotel's guests could travel from their train compartment to their hotel bedroom and back again without ever having to step out into the Askanischen Platz and outside weather. There was also an official railway ticket booth built in the hotel. When the renovations were completed, the Hotel Excelsior accommodated 600 rooms, 750 beds, 250 bathrooms, 9 restaurants, and a library. It also provided guests with 200 daily newspapers from around the world. The interior decoration included marble-covered walls and adornment by the Berlin-born artist Carl Langhammer (1868–1956). == Excelsior in Hitler's thirties ==