This photograph (by “Alkivar”) shows a reconstruction of the double helix model of DNA, constructed by James Watson and Francis Crick in 1953. The metal plates are molecular models of bases (some of these plates are original). The model is located in the Science Museum, London (see also their photograph).
This model not only led to one of the greatest-ever breakthroughs in biology (see the original 1953 paper, as PDF), but also demonstrated that “playing with models” was an effective way of doing chemistry. The discovery built on X-ray crystallography work by Maurice Wilkins, Rosalind Franklin, and Raymond Gosling (see their papers and the famous X-ray photograph produced by Gosling). Chemical investigations by Erwin Chargaff and others also produced essential information.
The breakthrough by Watson and Crick is commemorated by, among many other things, the Cambridge stained glass window shown below (located in the dining hall of Gonville and Caius College, photo by “Schutz”).