The Leuenhof, the former headquarters of the Bank Leu, is one of the most prominent commercial buildings of Zurich’s world-famous Bahnhofstrasse. It was built together with the Peterhof, its neighbour, between 1913 and 1916. The central ground floor boasts the magnificent client foyer, and the basement hides a supremely beautiful vault. Following a change of owner of the listed building, a design team under the lead of Architect Tilla Theus was tasked to modernise the office spaces in the upper levels and to convert the lower levels into retail space. As most historic iron-reinforced concrete buildings constructed in the early 1900s, it consists of frame structures with low shear reinforcement ratios and hourdis slabs. Furthermore, the earthquake resistance was not living up to today’s requirements. To protect the most valuable parts of the building interior an external stabilisation in the courtyard was identified as promising seismic rehabilitation concept. Through close collaboration with the architect and heritage specialists, the stabilising steel structure turned into a sculptural object. Strengthening the down beams of the floors while introducing a multitude of perforations for building services without damaging any of the important parts of the building was a major challenge solved with a combination of innovative design concepts and in-situ rupture testing. The paper outlines the rehabilitation project with a focus on selected structural design topics.