The edifice was built as a theatre by architect Wilhelm Vernukken in the years 1603/1606. The commissioner was Landgraf Moritz, who named the Ottoneum after his son Otto. Today, a natural history museum is housed here. Well-known collection pieces are a Xylotheque and the Ratzenberger Herbarium. [German]
In several German railway stations, there are model railway layouts where children (and their parents) can play with after putting in a 1 Euro coin. The layouts are pretty large and offer a lot of interesting details. Do you know similar layouts in your city and would you spend a Euro for having such fun?
As you know I love to stroll around railway stations while waiting for the next connection. So I do at airports as well. At Frankfurt on Main Airport I came across this Cadillac Sedan (1956) which is an advertisement for two German museums about technology.
Fun detail seen in Kassel: A figure standing on top of a sphere inside a church tower. Its a sculpture created by the artist Stephan Balkenhol. The traffic lights are not art, I was just standing at a pedestrian crossing and there was no time for a better position.
After World War II a large part of Kassel was rebuilt in the style of the 50ties. So if you are interested in the architecture of this period a walk through Kassel is a good way to learn more about it.