Julianapark is a relaxed neighbourhood park northwest of Utrecht's centre, with broad lawns, mature trees, water and a small animal area that makes it especially easy with children. It is not a major monument, but it shows a softer everyday side of the city.
Come when you want a pause from canals, museums and bicycles in the old centre. The park is most useful if you are staying nearby or exploring Zuilen, but on a sunny afternoon it earns the detour.