The oldest parts of the Zitadelle are the donjon Juliusturm and the Palais which were built in the 13th and 15th century. During World War II the area was used for military purposes.
The ancient arsenal houses a nice museum and it is definitely worth it to climb the wooden stairs of the Juliusturm. On the top you have a beautiful view over the west of Berlin where nature and city are close to each other. At the end of the day you should have a break in the historic tavern where you can enjoy the rustic atmosphere while eating with your hands (opened every day from 11:00, Sunday from 10:00).
The Zitadelle Spandau offers also many activities for kids, especially in the summer: Discovering the Middle-age, art classes in the Kunstbastion (School of arts), puppet theatre and many more events. Just have a look at the programme.
Source: Spotted by Locals