The Swiss shell pioneer Heinz Isler (1926–2009) fundamentally challenged established shell design methods by introducing original methods of form finding based on gravity. He realised elegant and pure shell forms in reinforced concrete, incarnating the perfect match of structural efficiency and form. With his shells, he gained acclamation of structural engineers and architects, and of the public. Heinz Isler’s more than 1400 built concrete shells are mostly located in Switzerland. The twin shell roof for the motorway rest area in Deitingen, Switzerland, and recent maintenance works to preserve this monument of structural art are described. After more than 50 years of use, the good condition and unaltered technical performance of the shells speak for Isler's excellent engineering work. The principle that well-designed structures are more durable is confirmed once again. Due to the non-invasive maintenance works carried out in 2016, the substance and aesthetics of the shells, which are one of the most successful and boldest engineering designs by Heinz Isler, are preserved for the shells to serve as a landmark on the motorway for decades.