The tower is leaning, also in reality. Its architect came from Germany (16th century) and was used to build on solid soil. This didn't work out well on the weak Friesian soil so during the building the tower started to lean. The further building upwards was more straight in an attempt to correct this, so the tower has also a slight curve (noticeable on the picture). Eventually the building was stopped because of collapse danger, and the architect dismissed. That's also the reason why the tower has no steeple.