Sort:  

you mean the white tower? It is the so called former Bergfried and is one of the landmarks Bad Homburg is known for. The tower is a 14th century's keep of original castle and located in the middle of the castle, and contains a museum these days. Original the tower was used to watch out for enemies, the main fortress for defence and also the former owners lived there as it was difficult to enter the building.

Awesome, I want one.