Nieuwe Kerk, the royal crypt and the tower
The burial church of William of Orange and the House of Orange-Nassau, including King William I and Queen Wilhelmina. The tower is the second-tallest in the Netherlands and can be climbed for a view over the rooftops and, on a clear day, all the way to The Hague.
One ticket covers both churches; the tower closes an hour before they do. Backpacks are not allowed up, and under-6s cannot climb at all.
Official site