My wife and I are Norwegian, and we plan to spend three months in Spain next winter. Will we need to register our stay with the Spanish authorities?
NO - As Norwegians, you have a right to stay in Spain for up to three months without any conditions or formalities other than the requirement to hold a valid identity card or passport.
You may have to anmeldelse af dit ophold to local authorities in other countries, even for stays shorter than three months; however, they can't ask you to register your residence.