My city Jena
The Jena Bismarckturm (means Bismarck tower) is a 21 meter high round tower made of limestone blocks made around 100 years ago as a memorial of visiting Bismarck of Jena.
This beautiful tower is located on the top of a hill, and from the area around it you have an astonishing view to the city.
Unfortunately the tower is closed and visiting inside or top of it is not possible. But it is still a beautiful building from outside which makes it definitely worth to visit.
More information [here].