Witch University is a castle created 10 centuries ago, then known as Cromwell Castle.
After Aggie Cromwell became an ordinary witch, the castle became an institute for young witches and warlocks.
Recently, Witch University enrollment was severely down, so Halloweentown Council and the School decided that for the first time in it's history they would admit non-witches/warlocks. The low enrollment of witches and warlocks has mainly Marnie Piper to blame, as she opened the portal between both worlds. Witches and Warlocks were required to use their magic, but when Marnie opened the portal between both worlds and non-witches and warlocks attended, they forbid the use of magic on school grounds.