Saint Martin's Cathedral of Utrecht (or Dom van Utrecht) is the cathedral with the highest tower (112 meters) in the country. Since a tornado passed by August the 1st, 1674, the cathedrale is split in two.
View from the tower of Saint Martin's Cathedral
The Oudegracht canal which traverses the whole city of Utrecht is absolutely gorgeous during fall. A fair part of Dutch people prefer the canal from Utrecht over the ones from Amsterdam (but I disagree :) ).