The construction project being studied is a government investment related to the relocation of a biomedical institute delivering research-based knowledge and contingency support in the fields of animal health, fish health and food safety. The project covers a total of 63,000 square meters distributed over 10 buildings with a very high degree of complexity. The design alone has required 1 million hours, which relates to a client cost of about 100 million Euro. The purpose of this paper is to study the applied methodology for managing the detailed design to identify lessons learned from the project. The theory underlying the study is inspired by lean design management and design theory linked to design as phenomena, including reciprocal interdependencies, iteration, decomposition, design as a “wicked problem”, learning, gradual maturation, etc. The article is based on an abductive research design and has been implemented as a case study where both qualitative and quantitative methods have been used.