The second phase of the Darwin Centre is an extension of the famous Natural History Museum in London, taking the form of a huge eight-storey concrete cocoon, surrounded by a glass atrium. The Natural History Museum is both one of the UK's top five visitor attractions, and a world-leading science research centre. The architecture of the Darwin Centre reflects this dual role, and reveals to the public for the first time the incredible range and diversity of the Museum's collections and the cutting-edge scientific research they support.The centerpiece is made to appear like a large silk cocoon, and forms the inner protective element that houses the museum?s unique collection of 17 million insects and 3 million plants. The shape and size give the visitor a tangible understanding of the volume of the collections contained within. The collections areas within the Cocoon are world class, the regulation of temperature and humidity reduce the risk of pest infestations ensuring that the collections will be protected and preserved for many years to come. The exposed thermal mass of the continuous sprayed reinforced concrete shell maintains a stable internal environment, and minimizes energy loading.Public access to the scientific core of the second phase of the Darwin Centre takes the form of a visitor route up and through the cocoon, overlooking the science and collection areas. Visitors can experience the Darwin Centre as a compelling and interactive learning space, observing the scientific and research activities without interrupting scientific work in progress. C. F. Mler Architects was chosen for the commission in 2001, in competition with 59 other international architectural firms.