The temporary multipurpose hall built by German architects Frei Otto (1925-2015) and Carlfried Mutschler (1926-99) for the 1975 Federal Horticultural Show in Mannheim ranks as the world's largest wooden grid shell construction. Working largely without any digital computation technology, Otto designed the building's complex roof using a delicate suspended model, oscillating between modeling, drawing and measurement, hand and eye, during the design process to create this unique structure.Drawing on largely unpublished materials from the archives of the architects, this book presents the history of this experimental building for the first time--at a crucial moment in the building's history. Although it was put under a preservation order in 1998, an international debate is now underway over the future of the structure: whether to maintain it, how to maintain it, and how best it can be used.