I like the German island of Sylt. Billund, Denmark as a good stop, as you can walk to Legoland from there. There's a hotel in walking distance too. We spent a night in Bornholm island off the coast of Sweden, very quiet and relaxed. Kalmar, Sweden has a super airport, and was very welcoming. If you continue north, Brattforsheden is a fascinating fly in museum, though grass runway.