Zonnestraal Sanatorium is a historic building located in the Netherlands, specifically in the town of Hilversum. Designed in the 1920s by architects Jan Duiker and Bernard Bijvoet, it was originally established as a tuberculosis sanatorium. The design reflects the principles of the De Stijl movement, emphasizing functionality and harmony with nature. The sanatorium features large windows and open spaces, allowing for ample sunlight and fresh air, which were believed to aid in the treatment of tuberculosis. Today, Zonnestraal Sanatorium is recognized as a significant example of modernist architecture and is a protected heritage site.