Formerly a water tower located inside the Stadtpark (City Park) is now housing Hamburg's planetarium. This is a beautiful place where nature and (popular) science come together. You can attend different shows, readings and even music events. It features a powerful projector, which lets you travel through time and space.
I did ask and I was shown the way up to the roof. No cover no guard and what a view I had after clinbimg up 8 stories through this building. Hamburg's buildings are hidden outside the park, but among all those trees. Its hard to believe how big this city is.