Blankenburg, Blankenburg am Harz, or Bad Blankenburg, city (1994 pop. 18,680), Saxony-Anhalt, E central Germany. It is a spa located at the northern foot of the Harz Mts. and is also known for its tree and seed nurseries, ironworks, and stone quarries. During his residence in Blankenburg (1837-45), the educator Friedrich Froebel founded the first kindergarten.