The object of the study is the restoration, restructuring and expansion of the listed V. Koulouras Megaron for its reuse as a Toy Museum. The limited space of the existing building is insufficient and can not serve the proper functioning of a museum and its needs for storage space, autonomous offices, archive and maintenance space. The addition of a new building, in extension of the existing one, is a necessary condition for the complete and autonomous operation of the Toy Museum and for the provision of spaces for periodic exhibitions, a library, educational programs and related events. Fundamental design principles of the new building are its formal affinity with the old in terms of materials, but also the contrast of volumes and style, with the aim of adding a modern background for the Megaron, clearly distinct from it, which combined to the preserved surrounding space complements its function while contributing to its promotion.