Æbelholt Kloster Museum covers the ruins of a medieval Augustinian abbey a few kilometres west of Hillerod. The site is modest, but the combination of ruins, herb garden, and archaeological finds gives a grounded picture of monastery life in North Zealand.
It works best as a quiet add-on after Frederiksborg Castle, especially if you are travelling by car or bicycle. The museum's displays on medieval illness, skeletons, and care for the poor make it more distinctive than another simple ruin.