Sonneberg in Thuringia, Germany, is the seat of the Sonneberg district. It is in the Franconian south of Thuringia, neighboring its Upper Franconian twin town Neustadt bei Coburg. Sonneberg became known as the "world toy city", and is home to the German Toy Museum and the Sonneberg observatory, founded in 1925. The Thuringian Slate Mountains border the city, with the Franconian Forest to the east.