Rügen is Germany's largest island, famous for its stunning chalk cliffs, especially the iconic Königsstuhl in Jasmund National Park. It's a perfect destination for families looking to explore natural beauty and outdoor activities, including snorkeling in the Baltic Sea. The island offers a mix of serene beaches, charming seaside resorts, and scenic hiking trails, making it an ideal spot for a memorable family vacation.

Copenhagen is a vibrant city known for its family-friendly atmosphere, rich history, and beautiful waterfronts. It's perfect for your 3-day stay with plenty of cultural attractions, delicious food spots, and relaxing parks to explore. The city offers a great balance of urban charm and cozy Scandinavian vibes, ideal for a family trip.

On your way back to Alphen aan den Rijn, consider stopping at the charming city of Münster in Germany. Münster offers a delightful blend of historic architecture, bike-friendly streets, and a vibrant cultural scene, perfect for a relaxing break during your journey. It's a great spot to stretch your legs, enjoy some local cuisine, and soak in the atmosphere of a traditional German town.